For the dough:
Lightly grease a large bowl. Mix the water, condensed milk, cream, oil, sugar and egg in a large measuring cup. Mix the flour, yeast and salt in the bowl of a stand mixer fitted with a dough hook. With the mixer on low, add the water mix. After the dough comes together, increase the speed to medium and mix until the dough is shiny and smooth, about 4 to 6 minutes. Turn the dough out on a floured surface and shape into a ball. Place in the greased bowl, turn over to grease the ball. Cover with plastic wrap and let set in a warm place until doubled in size.

For the filling:
Melt 1 Tbsp of the butter in a large skillet over medium heat. Add the beef and cook until just beginning to brown, 6 minutes or so, breaking up any large clumps. You want the hamburger to be uniform crumbs. Using a slotted spoon, transfer the meat to a paper towel lined plate.

Pour off all but 2 Tbsp of fat from the pan. Add the onion and cook until softened, about 3 minutes, then add the cabbage and toss just until it begins to wilt. Remove from the heat. Return the beef to the pan with the veggie mix, stir well and season with salt and pepper.

To assemble:
Adjust your oven racks to the upper middle and lower middle position, preheat to 350 degrees. Coat 2 baking sheets with cooking spray. Divide your dough ball into 8 equal portions (cut the dough ball in quarters, cut the quarters in half). Roll each piece into a 7 inch circle, and drape into a small deep cereal bowl (this acts as a form for your bun). Add a slice of cheese to the bottom of the bun, then add 3/4c of meat/veggie mix. Stretch and pinch the bun closed, then invert the bowl onto your hand and place the bun on the greased cooking sheet, seam side down. Note: be sure to pinch the bun closed well, or the cheese will leak out. Place four buns on a sheet, cover with plastic wrap and let rise until puffed, about 20 minutes.

Bake until golden brown, about 20 minutes, rotating the sheets half-way through the baking time. Brush with the reserved melted butter and serve.