Step 1

Preheat oven to 425 degrees F. Line a large baking sheet with parchment paper.

Step 2

Combine the broccoli with the olive oil and salt in large bowl. Toss to combine. Transfer to prepared baking sheet and arrange in a single layer.

Step 3

Roast in preheated oven for 15 minutes. Stir half way through cooking. Broccoli is done with tips start to turn dark brown.

Step 4

Melt butter over medium high heat in large sauce pan or dutch oven. Add mushrooms and onion. Stir to coat in melted butter and then allow to cook, undisturbed, until they begin to turn golden brown. Then stir occasionally until fragrant, about 8-10 minutes total.

Step 5

Add flour and constantly stir. Reduce heat to medium and allow to cook for about 4-5 minutes.

Step 6

Add the milk and salt, stir while scraping the bottom of the pan to loosen anything that sticks, and cook until slightly thickened, about 5 minutes.

Step 7

Remove from heat and stir in grated cheddar.

Step 8

Combine all topping ingredients in small bowl.

Step 9

Preheat oven to 400 degrees F.

Step 10

In large bowl (or the pan you used to make the cheese sauce), combine roasted broccoli with cheese sauce. Gently toss to combine. Transfer to a greased 9x13 baking dish. Sprinkle with crumb topping.

Step 11

Bake, uncovered, for about 10 minutes. Then broil for an additional 2-5 minutes to brown.