Start by heating a large pot of water to boiling. Core the cabbage and submerge it whole in the boiling water. Let it soften for 2 to 3 minutes before gently peeling off the outer leaves and setting them aside to cool.

Combine the ground beef, pork, cooked rice, finely chopped onion, garlic, and egg in a large mixing bowl. Season well with salt and pepper and thoroughly mix to form the filling.

Soak the dried mushrooms in hot water for 15 minutes until soft, then chop them finely. In a skillet over medium heat, melt the butter and sauté the fresh mushrooms until they turn golden brown. Stir in the flour and cook it for about one minute to create a roux.

Gradually add water to the skillet, stirring constantly to prevent lumps. Add the mushroom stock cube, the chopped dried mushrooms, and the sour cream. Season with salt and pepper, then simmer the sauce until it thickens.

To assemble, place around two tablespoons of the meat filling onto each cabbage leaf, fold in the edges and roll tightly. Arrange the rolls seam-side down in a large casserole dish.

Pour the prepared mushroom sauce evenly over the cabbage rolls. Cover the dish with foil and bake in a preheated oven at 350°F (175°C) for about 1 hour and 30 minutes, until the rolls are tender and cooked through.

Serve the Golabki warm with a generous amount of the mushroom sauce spooned on top. It pairs wonderfully with mashed potatoes or crusty bread.