Boil 3-4 lasagna sheets in boiling water for about 8-10 minutes until ready, then immediately place them in cold water to prevent sticking.
Prepare the minced meat by frying it in a pan with chopped onions, olive oil, and black pepper until crumbly, then add the tomato juice and simmer for 20 minutes until thickened.
Make the béchamel sauce by melting the butter, then frying the flour for about 2 minutes. Add the fresh milk and stir until the sauce thickens.
Layer in a rectangular baking dish: start with béchamel sauce, then lasagna sheets, more sauce, minced meat, and repeat until all sheets are used.
Top with béchamel sauce, generously cover with cheese, and bake in a preheated oven at 220°C until golden brown.