Preheat the oven: Preheat your oven to 375°F (190°C). Grease a baking dish with olive oil or butter.
Cook the cauliflower: Steam or boil the cauliflower florets until tender, about 8-10 minutes. Drain well and set aside.
Prepare the creamy sauce: In a medium bowl, whisk together the heavy cream, sour cream, minced garlic, Dijon mustard (if using), salt, and pepper. Stir in the shredded cheddar cheese and half of the Parmesan cheese.
Assemble the bake: Place the cooked cauliflower florets in the greased baking dish, then scatter the diced ham evenly over the cauliflower. Pour the creamy cheese mixture over the top, making sure everything is well-coated.
Top with cheese and bake: Sprinkle the remaining Parmesan cheese over the top. Bake in the preheated oven for 20-25 minutes, or until the top is golden and bubbly.
Serve: Garnish with freshly chopped parsley and serve hot. This dish can be enjoyed as a main course or a hearty side to complement any keto- friendly meal.