Chop half of the mushrooms finely and shred the other half. Set aside.
Cover the onions lightly with plastic wrap and microwave for 1 to 2 minutes. Set aside to cool.
Soak the breadcrumbs in the milk.
In a large bowl, combine the ground meat, onion, milk-soaked breadcrumbs, egg, salt, pepper, and nutmeg. Mix together using your hand until all combined. Divide into 4 equal patties.
Heat a non-stick frying pan on medium high heat. Place the patties down and press down to create a dip in the center.
After the patties develop color, flip, cover the pan, and cook on low heat for 6 minutes.
Take the lid off and add the mushrooms and garlic. When the mushrooms are all covered in the grease, add the cream and cook until it thickens slightly. Taste for salt and pepper.
Plate up and spoon over the cream sauce.