Heat oven to 400°F.

Bring a large pot of water to a boil over high heat. Add broccoli and cook until crisp-tender, about 3 minutes. Remove with slotted spoon.

Add cauliflower and cook 7 minutes until crisp-tender. Drain, reserving 1/2 cup cooking liquid.

In a medium saucepan, melt butter over medium heat; whisk in flour until blended. Gradually whisk in milk, cream and reserved cooking liquid. Cook 1 minute whisking continuously, until thickened; add in spices. Remove from heat and stir in egg yolk and 1 cup of the cheese.

Layer broccoli and cauliflower in a 15 x 10 inch baking dish, alternating each. Spoon sauce evenly over veggies and sprinkle with remaining cheese.

Bake at 400°F for 20 minutes.