Preheat oven to 400°

Cut cauliflower into small bite-size florets and place on a sheet pan. Drizzle with olive oil then season with salt and pepper, to taste. Roast 15 - 20 minutes or until fork tender. Set aside.

In a large pot, melt butter over medium high heat. Add onion and cook 3 - 5 minutes, stirring frequently, until softened and fragrant.

Add garlic and continue cooking an additional 1-2 minutes. Add flour and stir vigorously to thicken.

Pour in mik 1/2 cup at a time, whisking well after each addition. Continue whisking and add in the broth. Add roasted cauliflower to the pot.

Remove from heat and gently stir in Pepper Jack and Cheddar cheeses. Adjust seasoning to taste and serve warm.