Melt butter in a saucepan, add the flour & mix for a few minutes until it forms a paste. Slowly pour in the milk a little at a time & stir as you cook it to the consistency of a thin custard. Simmer for 5 minutes, add crumbled gorgonzola & simmer until melted & incorporated. Add 1/2 cup to the filling, season with salt, pepper & smoky ranchero seasoning.