First, unfroze spinach (you can use the microwave). Heat the olive oil and add the spinach, seasoning with some black pepper. Cook and set aside. Preheat the oven to moderate (180ºC). Put the fish fillets on a greased ovenproof dish. Add the sparking wine and cover with waxed paper slightly wet. Bake it for 15 minutes. Remove from oven and set aside. Prepare the sauce: Heat the olive oil in a saucepan. When itâs hot, add the flour and mix well. Slowly stir in the vegetable bouillon and the sauce from the fish, seasoning with black pepper and nutmeg. Let it boil in moderate heat, always stirring. Mix the yogurt with the egg yolks and carefully stir in the sauce. Spread the spinach on the ovenproof dish. Set fish on top. Add the sauce and pour on some grated Parmesan cheese. Take it to the over until itâs golden brown on top.