Preheat oven to 350 degrees. Butter the bottom and sides of a 9x13 baking dish with one tablespoon of butter.
Add the broccoli and cauliflower to the buttered dish and sprinkle with 1/2 teaspoon of salt and 1 teaspoon pepper.
Bake for 20 minutes, stirring once halfway through.
Start the cheese sauce when the vegetables have 8 minutes left to bake.
To make the cheese sauce, melt the remaining 3 tablespoons of butter in a medium sauce pan.
Add the garlic to the melted butter and cook, stirring constantly, for 1 minute.
Whisk in the flour, remaining teaspoon of salt, and remaining teaspoon of pepper. Cook for 1 minute.
Slowly add the milk to the flour mixture, whisking constantly. Cook, whisking constantly, for 4-5 minutes or until mixture reaches the consistency of a thin gravy.
Remove from the heat and whisk in the grated Roth Original Havarti Cheese until the sauce is smooth and creamy.
Remove the vegetables from the oven and stir. Pour the cheese sauce evenly over the vegetables and sprinkle the top with the Panko bread crumbs.
Return to the oven for 10 minutes.
Place the pan under the broiler and broil until the bread crumbs are browned, about 2 minutes.
Remove from the oven, sprinkle with parsley, and serve.