Whisk together the sugar, yeast and water. Let sit for 5 minutes to "proof" (meaning to check and make sure your yeast is active before you waste any more ingredients!) The yeast, sugar and water should start to bubble just a bit.
Stir in the milk, oil, 1/4 tsp salt and eggs. I use my KitchenAid mixer with a bread hook to mix up bread so I proofed everything in the mixing bowl, then added the other ingredients. Put about 3 cups of the flour into the bowl and turn the mixer on to a low setting. Let the mixer incorporate most of the ingredients together then add the last cup of flour, about 1/4 cup at a time until it pulls away and makes a nice elastic-looking ball. Keep the mixer on for 5 more minutes or so. (You can of course do this by hand.)
Llet the dough rise for about an hour. If your house is warm, you can do this on the counter. If your house is a bit cool, turn your oven onto warm for a few minutes, then turn it off. Rub a bit of oil in the bottom of a bowl and turn the dough into that bowl, flipping it around and turning it so that all sides are coated very lightly with oil. Cover the bowl with a clean kitchen towel and let rise until doubled, about an hour.
Filling
In a skillet, heat the oil then add the onion and ground meat. Cook, stirring, until the onion is softened and the meat is no longer pink. Add the cabbage and cook a few more minutes until the cabbage wilts. Salt and pepper the meat mix and set aside to cool, covered.
Assembling
When the dough has been rising an hour or so, check that it is ready by poking two fingers into it. If the indentations from your fingers remain in the dough, it's ready! Punch the dough down, cover and let rest 5 minutes. Meanwhile, cover a cutting board or counter with a light dusting of flour.
Divide the dough in half and roll one half into a roughly 10 x 7 inch rectangle. Cut this into six squares and place about 1/4 cup of the meat and cabbage mix into the middle of each square. Pull two opposite corners together and pinch together, then do the same with the other two corners. Place seam side down onto a baking sheet lined with parchment paper. Repeat with the other half of the dough.
Preheat the oven to 375 while you cover the bierocks again and let rise about 20 minutes.
Uncover and bake about 15 minutes. Cool a bit on wire racks then serve.
Notes
If you want to freeze them, let them cool completely and wrap each bierock individually in foil, then drop them all into a freezer bag.