Melt the butter in a large oven-safe rondeau. Add in the onions and bell pepper and cook until softened. Add in the garlic and cook until fragrant, about a minute more. Add in the chile powder and cook for another minute. Add in the hominy and stir until combined. Pour in the chicken stock and add in the thyme; simmer until reduced slightly.
Add in the cream and bring to just a simmer. Stir in the cilantro, lemon juice, salt and pepper. Stir in the milk. Cover pan and bake for about 20 minutes, stirring a couple of times during baking, until the baked hominy is hot and mixture is bubbling.