1 cup (250 grams or 2 sticks) butter, room temperature
1 cup (250 grams) sugar
6 eggs, separated
2 cups (250 grams) buckwheat flour (this comes in light or dark, so be aware the choice will affect the color of your cake)
2 1/4 cups (250 grams) almond meal, skins on if possible
1 apple, peeled and grated
1 vanilla pod
7 ounces (200 gr) lingonberry jam (redcurrant or cranberry jelly can also substitute)
1/2 tablespoon icing sugar for dusting
Cream together the butter and sugar. Add the egg yolks and beat until pale and creamy. Add the buckwheat, almond meal, grated apple and the scraped seeds of the vanilla pod until just combined.
Beat the egg whites to stiff peaks. Gently fold in, bit by bit, into the batter until well combined and pour batter into a greased and lined round baking tin (10 inch diameter).
Bake in a medium oven at 350ºF for about 50 minutes or until the cake is deep golden brown on top and a skewer inserted in the middle of the cake comes out clean. When cool enough to handle, remove cake from tin and slice in half lengthways. Spread the bottom layer with the lingonberry jam and replace the top layer. Just before serving, dust with powdered sugar.