Bring a large pot of salted water to a boil. Core the cabbage and carefully peel off 12-14 large intact leaves. Blanch leaves for 3-4 minutes until pliable but not mushy. Transfer to ice water, then drain and pat very dry. Roughly chop the remaining cabbage core and reserve 2 cups for the base.

Heat a large skillet over medium-high heat. Add the ground beef and cook, breaking it up, until browned and just cooked through, about 6 minutes. Add the diced onion and cook until softened, 4 minutes more. Stir in the garlic and cook 30 seconds until fragrant. Remove from heat and let cool 10 minutes.

Transfer the cooled meat mixture to a bowl. Add the cooked rice, beaten egg, paprika, pepper, and 0.5 tsp salt. Mix gently until just combined - do not overmix or the filling gets dense.

In a small saucepan, combine the tomato sauce, brown sugar, vinegar, and Worcestershire. Bring to a simmer over medium heat and cook 5 minutes to meld flavors. Taste and adjust sweetness or tang to your liking.

Preheat oven to 350F. Grease a 9-inch springform pan. Spread 0.5 cup sauce on the bottom. Arrange the chopped cabbage in an even layer. Line the pan sides with blanched leaves, overlapping slightly and letting excess hang over the edge. Pack half the filling into the center and press gently. Pour 0.75 cup sauce over. Add remaining filling, press smooth, and fold overhanging leaves to cover the top. Spread remaining sauce evenly.

Place the pan on a foil-lined baking sheet to catch drips. Bake 55-60 minutes until bubbling at the edges and a thermometer inserted in the center reads 160F. Let rest 15 minutes before releasing the springform and slicing.