Makes 1 cup
Gently heat milk in a small saucepan just until barely simmering. Remove from heat and keep covered.
Melt butter in a small saucepan. When foam subsides, add flour and stir until smooth. Cook 1 to 2 minutes, stirring; do not allow flour to color. Gradually add warm milk, whisking to combine. Add salt and cayenne and increase heat to medium. Cook mixture, whisking continuously, until sauce comes to a boil and is thickened. Remove from heat and add 10 roasted garlic cloves. Pour hot mixture into a blender, cover tightly, and process until smooth. Transfer to a small bowl and cool slightly, placing a piece of plastic wrap directly on the surface to keep a skin from developing.