Preheat oven: Preheat the oven to 375°F (190°C) and either grease your muffin tin with olive oil to avoid sticking.
Prepare the mixture: In a large mixing bowl, combine ground beef, almond flour, egg, parmesan cheese, onion, garlic, and seasonings. Mix gently to avoid tough muffins.
Fill the muffin tin: using a spoon evenly divide the mixture between the muffin tins and press down lightly so they take form but not too firm.
Add the toppings: Brush a little sugar-free ketchup over each muffin for flavor and moisture.
Bake the muffins: Slide into the oven and bake for 20–25 minutes, until the tops are golden and the centers register 160°F.
Rest and serve: Let the muffins rest for 5 minutes before removing and serving.