Melt butter over low heat, add flour and mix rapidly. Add milk gradually and continue stirring until mixture thickens. Remove saucepan from heat and add grated Provolone Valpadana DOP, black pepper, salt, and egg yolks. Beat egg whites into peaks and gently fold into milk and cheese mixture. Fill 8 buttered molds and bake in a bain-marie in preheated 180° C oven for about 20 minutes. Serve immediately.