Â Spread mixture evenly over Â bottom of a 2-quart casserole.
Â Melt butter in a small saucepan. Whisk in flour, and cook over medium-high heat. Add broth and cream and whisk until thickened, about 5 minutes. Season lightly with salt and pepper and pour over spinach.
Â Arrange Â polenta slices on top of spinach and sauce in overlapping concentric circles, pressing to submerge Â polenta slightly. Sprinkle Â shredded cheeses over Â polenta. Cover with foil and bake Â 30 minutes. Remove from oven and preheat broiler.
Â Uncover polenta and broil 6 inches from Â heat about 2 minutes or until browned and bubbly. Let stand 10 minutes before serving.