Stir together the ground flaxseed and water, and let it soak for 5 minutes to make a 'flax egg'.
Mix the flour, ground hazelnuts, sugar, baking powder, vegan butter and flax egg and using your hands, knead into a smooth dough.
Shape the dough into logs about 3 cm thick (1 - 1.5 inches). To a make a firm log that holds together well, squeeze the dough into shape, then gently roll on a board with your palms to get an even circular shape.
Cover the dough logs with a tea towel and refrigerate for at least one hour.
Shape and bake
Preheat the oven to 180°C (355°F).
Cut the logs into slices of just under 1cm or about ¼ inch.
Top one side of each slice with some chopped hazelnuts. Either just press the raw cookies top down into the chopped hazels, or place a small amount on top of each and gently firm down.
Place cookies on a baking tray lined with baking parchment or reusable baking sheet. You don't need to leave a lot of space between them.
Bake at 180°C (355°F) for 15-20 minutes, until the rim of the cookies are golden brown.
For most consistent and best results, ingredients should be weighed. These instructions are for the 'plain version' of our hazelnut cookies. For cocoa edged or chocolate dipped variations see the post above.