Whisk together all-purpose flour*, black pepper and salt in a shallow bowl. Crack 2 eggs into another shallow bowl & also whisk.
Portion (cut) cod fillet, season with salt and pepper to your liking, then get a piece of cod, dip in the egg mixture ( make sure it is fully coated on both sides) & drag it in the flour back and forth to coat completely. Repeat the same procedure with all the pieces of cod, then allow to rest in the fridge for 10-15 minutes.
Heat the peanut oil in a deep, ovenproof skillet over medium-high heat.
Fry the cod pieces over medium heat 8 minutes (4 minutes per side). Transfer to the plate (you might need to fry the coated cod pieces in batches).
Making sauce:Melt 2 tbsp. butter in a large pan, stir in the flour, then pour the warm milk and whisk with a wire whip. Cook 4-5 minutes, stirring continuously. Remove from the heat & gradually add the egg yolks, whisking constantly to prevent curdling. Put back on the heat and bring to a boil, whisking the sauce constantly for another 1-2 minutes until it becomes thick.
Add the cream & baby spinach leaves. Cook 2-3 minutes or until all the spinach is wilted. Season with the black pepper and stir in the lemon juice.
Transfer the fried cod pieces into the sauce.
Bon appétit!