Preheat your oven to 350°F (175°C). Prepare your baking dish with cooking spray or butter.

Bring salted water to a rolling boil in a large pot.

Blanch broccoli and cauliflower for about 5 minutes until tender-crisp. Drain and plunge into ice water.

Combine sour cream, mayonnaise, Dijon mustard, garlic powder, onion powder, and half of the cheddar in a bowl until smooth.

Fold the cooled vegetables into the sauce until well coated.

Spread the mixture into a greased 9x13-inch casserole dish.

In a separate bowl, mix breadcrumbs, melted butter, remaining cheddar, and Parmesan until breadcrumbs are coated.

Sprinkle the breadcrumb mixture over the casserole evenly.

Bake for 25-30 minutes, until the topping is golden brown and bubbly.

Allow to rest for several minutes before serving.