Preheat oven 400º
Melt butter in a small saucepan over medium heat. Whisk in the flour until smooth.
Add milk, cream, salt, pepper and cayenne pepper and continue whisking until mixture comes to a low boil. Reduce to a simmer and stir in cheddar and fontina cheese until smooth. Remove from heat.
Meanwhile bring a small saucepan with 1-inch of water to a boil. Steam broccoli just until bright green, about 5 minutes. Remove from heat.
Grease a casserole dish. Add broccoli and fold in cheese sauce so all the broccoli is well coated. In a small bowl, mix panko crumbs, parmesan cheese and olive oil. Sprinkle over broccoli mixture.
Bake at 400º for 15 to 20 minutes.
Cheese sauce should be bubbly and bread crumb mixture well toasted.
Remove from oven, let sit 5 minutes before serving.