Mix the flour, salt and yeast in a bowl. Add the water and oil, mix and knead to form a soft, smooth dough. Knead in the spinach and 3/4 of the feta. Cover and leave to rise at room temperature for approx. 1 1/2 hrs. until doubled in size. On a lightly floured surface, roll out the dough into an oval approx. 2 cm thick, transfer to a baking tray lined with baking paper. Using your fingers, press holes into the surface, drizzle with olive oil and sprinkle with salt.
Bake for approx. 25 mins. in the lower half of an oven preheated to 220°C.
Melt the butter, cook the flour and cinnamon for approx. 2 mins., stirring constantly. Add the stock, bring to the boil, simmer over a low heat for approx. 15 mins. Stir in the sour single cream, add the beetroot and heat gently. Plate up the soup and garnish with the remaining feta and beetroot sprouts. Serve with the spinach & feta focaccia.