Potato, Cauliflower, and Onion Bake

The potatoes and onions harmonize with the cauliflower in this recipe, making for a slightly different twist on a classic bistro side.

Serves: 8Hands-on: 15 minutesTotal: 1 hour 20 minutesDifficulty: Medium

Serves: 8


  • 1 Tbsp. olive oil
  • 2 medium sweet onions, diced
  • 2 cloves garlic, minced
  • 3 Tbsp. butter
  • 3 Tbsp. flour
  • 3 cups 2% milk
  • 1⁄2 tsp. salt
  • 1⁄4 tsp. pepper
  • 1⁄2 tsp. mustard powder
  • 1⁄4 cup shredded Gruyère cheese
  • 2 lbs. russet potatoes
  • 4 cups cauliflower, cut into miniflorets


  • Preheat oven to 350°F and spray a 9-by-13-inch casserole dish lightly with nonstick spray.
  • Heat olive oil in a medium nonstick skillet over medium-low heat. When hot, add onions and garlic and cook, stirring occasionally, until tender, 10 to 15 minutes. Do not let onions brown.
  • While vegetables are cooking, heat butter in a medium saucepan over medium heat. When melted, add flour and stir to combine. Slowly stream in milk, whisking constantly to avoid lumps. Whisk in salt, pepper, and mustard powder. Simmer sauce, whisking often, until thickened, about 3 minutes. Remove sauce from heat and whisk in Gruyère cheese.
  • Peel and slice potatoes into 1⁄8-inch-thick rounds and spread them evenly along the bottom of the casserole dish. Layer onion mixture over potatoes, then spread cauliflower over onions. Pour sauce mixture over vegetables, cover tightly with foil, and bake until potatoes are just tender, 45 minutes.
  • Remove the foil from the casserole and bake an additional 15 to 20 minutes until the top of the casserole is browned and bubbly and vegetables are completely tender. Allow casserole to rest for 10 minutes before slicing.