Preheat oven to 400°F (204°C). Lightly grease an 8x8-inch baking dish.
Cook bacon in a skillet until crispy. Remove and set aside. Reserve bacon grease.
Boil cauliflower in a separate pot for 5 minutes, then drain and set aside.
In the skillet, add olive oil, onion, and garlic to bacon grease. Sauté until soft.
In a bowl, whisk milk and flour until smooth. Pour into skillet, bring to simmer.
Add cheddar, parmesan, and salt. Stir until melted into a creamy sauce.
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