Bacon Swiss Potato Cauliflower Casserole

Step 1
Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9×13-inch casserole dish.

Step 2
Place potatoes and cauliflower into a large pot and cover with water; bring to a boil. Reduce heat to medium-low and simmer until tender but firm, about 20 minutes. Drain and transfer potatoes and cauliflower to the prepared casserole dish.

Step 3
Heat olive oil in a skillet over medium heat; cook and stir onion in the hot oil until transparent, 5 to 10 minutes. Transfer cooked onion to the potato mixture.

Step 4
Place bacon in a large skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain the bacon slices on paper towels and crumble over potato mixture, reserving bacon grease in skillet.

Step 5
Melt butter into bacon grease in skillet over medium-low heat; whisk flour into butter-bacon grease mixture. Gradually stir cream into flour mixture until smooth; add milk if cream sauce is too thick. Whisk half the Swiss cheese, half the mozzarella cheese, garlic powder, salt, and pepper into cream sauce until cheeses are melted.

Step 6
Pour cream sauce over potato mixture and toss to coat; top with remaining Swiss cheese and mozzarella cheese.

Step 7
Bake in the preheated oven until casserole is bubbling and cheese is lightly browned, about 30 minutes.