Crumble the yeast into a large bowl. Add the water and stir until the yeast dissolves. Add the brown sugar, salt and buckwheat flakes. Gradually work in the rye flour, followed by the plain flour, until the dough comes away from the sides of the bowl. Cover with a tea towel and leave to rise for 20 minutes. Put the dough on a floured surface and knead until smooth. Divide the dough into four equal pieces and shape them into lengths. Place the lengths in a large roasting pan covered with baking parchment. Cut out strips of baking parchment and put them between the loaves to stop them sticking together. Leave to rise for 20-30 minutes. Bake in the lower part of the oven at 200°C for about 40 minutes.
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