Wash the spinach well and blanch it in boiling, salted water. Take it out of the water, pour cold water over it and drain well. Chop it finely.
Separately, beat 1 egg with salt to taste, 2 tbsp oil, 3 tbsp yoghurt and 1 tsp baking powder. Add the blanched spinach and torn leaves of fresh spearmint.
Stir well and gradually add the 3-4 tbsp flour, spoon by spoon, or as much as you need to get a dough slightly thicker than a cake one.
Fry the fritters in a nonstick pan that you've oiled lightly (oil the pan with a brush; 1 overflowing tbsp of dough is enough for 1 fritter).
Turn the fritters to redden equally on both sides. Pour the dough into the pan, while using 2 spoons to help you form the fritters more easily.
Serve the ready fritters with a yoghurt sauce or as a side to fresh lettuce salad.