In a blender, blend the milk with 6 tablespoons flour and 3 tablespoons melted butter. Pour into a heavy-bottomed saucepan. Season with salt and pepper. Cook over medium heat, stirring constantly until the mixture boils and thickens. Remove from heat, let cool, and then refrigerate.
In a separate pan, sauté the garlic and onion in 1 tablespoon of butter. Add the shrimp and sauté until they turn pink. Add the parsley and paprika. Season with salt and pepper. Allow the shrimp mixture to cool.
Once cool, mix together the shrimp with the previously-made white sauce. Form mixture into oblong croquettes. Dredge in flour, then beaten egg and, lastly, bread crumbs. If you want the croquettes to be crunchier, you can dip them a second time in the egg and breadcrumbs. Refrigerate for at least 1 hour.