For the wafer dough, clean, wash, peel and finely grate the beetroot. Cream butter with the whisks of the mixer. Stir in the eggs and 1 tbsp. flour in turns one after the other. Mix yoghurt and 6 tbsp. water. Mix the rest of the flour, baking powder and 1⁄2 TL salt. Alternating with yoghurt, stir into the butter-egg cream. Stir in beetroot.
Heat a double waffle iron (approx. 15 x 18 cm waffle surface) and brush well with oil. Bake a total of approx. 8 waffles, but add 1-2 tbsp. of dough per waffle iron side (the dough should not fill the waffle iron surface) and bake for 3-5 minutes. Keep the waffles warm in a hot oven (electric cooker: 80 °C/circulating air: 60 °C/gas: see manufacturer) until they are all baked.
Crumble the feta to serve. Chop the nuts. Serve waffles with feta, nuts and syrup. Sprinkle with chilli as desired.