The method might seem lengthy at first, but is actually quite simple, quick and easy at all stages of preparation. The final cake is more than worth it!
Preheat a fan oven to 180˚C. Prepare two greased and lined cake tins of the same size. (See recipe notes for useful info about using tins with and without removable bases, springforms, or if you don't have two cake tins the same size.)
Combine flour, cocoa powder, bicarbonate of soda, and salt.
Dissolve the sugar in hot (boiling) water, add oil and vinegar.
Combine your dry and wet parts and stir or whisk into a smooth batter.
Roughly divide up into the two cake tins and bake for about 15 minutes, or until a cake testing needle comes out clean.
Take the cakes out of the tins and onto a cooling rack. Let cool down for about an hour. (See recipe notes for tips about cooling and levelling dome-shaped cakes.)
Filling with Jam
TIP: From here on, keep working with the cake on the cooling rack or cake rack, with a tray or large plate underneath to catch excess jam and chocolate glaze dripping from the cake.
Gently heat the jam up a bit (on the hob or in the microwave) to make it more liquid and spreadable. This will also help it adhere to the cake and make it richly moist.
Spread a good layer of jam on the layer of the cake that will be the bottom. (At this point, you can also seal and conceal minor cracks and holes in the cake and piece a layer together that has broken in two or three pieces.)
Place the second layer of cake on top and use the rest of the jam to cover the whole top and the sides of the cake.
Let the jam cool down and set for a bit (around 15 min).
Break the chocolate into small pieces.
In a cup or jug, place sugar, water and chocolate together in the microwave on max power for 30 seconds. Stir until the chocolate is all melted and the texture is smooth. If chocolate does not melt, heat up again in steps of 15 seconds. (For other methods, see recipe notes.)
Let cool down a bit, stirring frequently to check consistency. You are aiming at a rather thick, but completely liquid chocolate mixture, that coats the back of a spoon about 3 mm thick.
Pour the glaze over the cake to cover it in a thick layer. Work your way round the sides with a cake spatula if necessary.(See recipe notes for some tips and detailed method.)
For best results and a less messy eating experience, wait for a few hours until the glaze has set.
Cut with a clean, hot knife (out of cup of hot water and wiped dry) for the most beautiful slices.
Bicarbonate of Soda
To substitute for bicarbonate of soda, use three times as much baking powder. So, instead of half a teaspoon of bicarb, use one and a half teaspoons baking powder.
Springforms and some cake tins have a base plate that can be separated from the round side walls of the tin. In this case, it is enough to grease the tin. After baking, go round the sides, take the base with the cake out and go round the bottom of the cake as well.If your cake tins do not have removable bases, we strongly recommend lining their bottoms with circles of baking paper. Otherwise, the cake will most likely stick badly to the base. Just go round the sides with a knife after baking, and the cake comes right out of the tin. Don't get rid of the baking paper too soon - it might still come in handy for levelling dome-shaped cakes (see below)
Baking the cake in just one tin
If you don't have two cake tins of the same size, or for whatever other reason want to bake the cake all in one tin - you can! Increase baking time to at least 20 minutes and check that a cake tester comes out clean before you take it out of the oven.You can cut the cake horizontally into two layers after it is baked and cooled down. Professionals use a wire cutter, but a large bread knife will also work.
Levelling the cake
In our experience, this cake rises well and creates a slightly domed shape.Some people cut of a thin layer off the top of their cakes to level them - but you lose a lot of cake in doing so! Here's what we prefer:When we let the cake cool down on a cooling rack, we flip it upside down. The weight of the cake pushed down onto the dome and helps to level it a bit. Baking paper underneath prevents the cake from sticking to the rack and leaving it engraved with the grid shape.Consider using the underside of one of your cake layers as the top of your cake - that way you will have a completely level cake top, which yields the most beautiful results for glazing - unlike our one here! (Well, you always know better afterwards!) It just makes it slightly trickier to fill the gap between the layers with jam.
Preparing the glaze
The above method is our 'lazy way' of doing it. Here are two other options:Option 2 (medium): Use boiling water (from a kettle) to dissolve the sugar. Once completely dissolved, add the chocolate, cover for a minute. Stir until chocolate is fully dissolved and consistency is smooth.Option 3 (crafty): In a small saucepan, dissolve the sugar in the water on medium heat and gently boil for a few minutes to create a sugar syrup. In the meantime, melt the chocolate in a bowl over a hot water or steam bath (bain marie).
Pouring the glaze
Temperature and runniness:
It really works best if the glaze is not too hot and runny anymore, or most of it will just run off the cake and only leave a thin layer. In particular, it is easier to cover the sides of the cake in a good layer of glaze if it has thickened up considerably.
Don't worry too much at this point about the glaze being too thick to create a completely smooth surface. If you run it off a spoon back into the jug or cup, and it melts back in within a few seconds, you're all good. Also, see below.
Keep some of the glaze back at first to patch up gaps, especially on the sides.
I (Paul) like to start with a big pool in the middle of the cake. Then I slowly make my way around the cake, pouring the glaze close enough to the edge to make it flow thickly across and onto the sides in a sort of rolling motion. Add a bit more where needed. To finish up, work your way round the sides with a cake spatula or wide rounded knife.
If there are some inconsistencys and wrinkles in the surface when you are done (like where you patched up a whole or there's a trace from using the spatula), a little shake of the rack or plater under the cake can help smooth them out.
Choice of chocolate
The traditional glaze for a Viennese Sachertorte uses chocolate with about 50% cocoa, and much more sugar. We found that waaay too sweet.We settled on 70% cocoa because it tastes amazing (like chocolate, not just sugar) and yields the most beautiful, glossy results.We also experimented with dark cook's chocolate (50% cocoa), which sets quicker, is sweeter, less smooth and more matt-looking, but closer to the traditional version. Just not as nice, we think!But just so you know, if you haven't got 70% dark chocolate on your hands or would rather just eat it as is, other types of chocolate will basically also work.Happy baking! :)