Thaw the spinach. Cut the feta into small pieces. Preheat the oven to 180 ° C (convection 160 ° C).
Mix the flour with baking powder and salt. Whisk the eggs with oil, buttermilk and spinach and quickly stir in the flour mixture. Finally fold in the feta cubes.
Pour the finished dough into the wells of the muffin pan and bake for 15-20 minutes. Let rest in the tray for about 5 minutes and then serve warm.