Preheat the oven to 400°F (200°C). Lightly grease a 9x13-inch baking dish with butter.

Heat the vegetable oil in a large skillet over medium-high heat. Add the ground meat and cook, breaking it up with a spoon, until well browned and no longer pink, about 6–8 minutes.

Add the chopped onion to the pan and sauté until softened and lightly golden, about 3–4 minutes. Stir in the minced garlic and cook for 30 seconds until fragrant.

Stir in the tomato paste and cook for 1 minute, then add the paprika, oregano, thyme, pepper, and salt. Mix well so the spices coat the meat.

Pour in the broth and bring to a simmer. Let it cook for 3–4 minutes so the liquid reduces slightly.

Stir in the heavy cream and mixed vegetables. Simmer gently for another 3–4 minutes until the sauce is creamy but still pourable. Taste and adjust seasoning if needed.

Spread the meat and vegetable mixture evenly in the prepared baking dish. Sprinkle the shredded cheese evenly over the top.

Arrange the frozen kroketten in a single, tight layer over the cheese, covering the entire surface of the dish.

Place the baking dish on the middle rack of the preheated oven and bake for 30–35 minutes, or until the kroketten are golden brown and crisp and the sauce is bubbling around the edges.

Remove the dish from the oven and let the casserole rest for 5–10 minutes before serving so the layers can set slightly.