How to make
Blanch the spinach in boiling hot salted water, drain it and cool it down. Add the feta cheese, the black pepper and the yellow cheese. Place a pot on the stove, put the milk and bring it to a boil.
In another pot melt the butter and gradually add the flour while stirring constantly. When the butter and flour made incorporated and the flour is cooked, pour the milk gradually and keep stirring until the bechamel gets the desired consistency.
When the bechamel is ready add a small quantity of the filling to it and mix well. Spread some filling on the bottom of a baking tray, place a sheet of lasagna on top and add some filling again.
Keep adding filling and lasagna sheets. The last layer should be lasagna sheet and bechamel on top. Grade the yellow cheese and bake your vegetarian lasagna in a preheated oven to 390°F (200 degrees).