Ingredients

4 tablespoons (1/2 stick) butter
1/3 cup minced onion
2 large garlic cloves, minced
1/2 teaspoon dry mustard
4 tablespoons Dijon mustard
2 1/2 cups fresh breadcrumbs made from crustless sourdough bread
1 cup (packed) grated Parmesan cheese (about 3 ounces)

12 to 13 cups broccoli florets (from about 3 pounds broccoli crowns)

1/2 cup whipping cream

Directions

BROCCOLI GRATIN WITH MUSTARD CHEESE STREUSEL:

Melt butter in large nonstick skillet over medium-high heat. Add onion and garlic; sauté until onion is soft, about 4 minutes. Mix in dry mustard, then 2 tablespoons Dijon mustard, blending well. Add breadcrumbs; sauté until crumbs are crisp and golden, stirring and pressing with back of fork to separate, about 8 minutes. Season with salt and pepper; cool completely. Mix in 3/4 cup cheese.

Cook broccoli florets in large pot of boiling generously salted water until crisp-tender, about 3 minutes. Drain. Transfer to paper towels; cool. (Streusel and broccoli can be made 1 day ahead. Cover separately and refrigerate.)

Preheat oven to 350°F. Butter 13x9x2-inch glass baking dish. Place broccoli in large bowl. Add whipping cream, remaining 2 tablespoons Dijon mustard, and 1/4 cup cheese; toss to coat evenly. Arrange broccoli in prepared dish. Sprinkle streusel over. Bake until broccoli is heated through and streusel is browned, about 30 minutes.