Melt 2 tablespoons of unsalted butter in a large, heavy pot over medium-high heat.

Add the chopped bacon and cook, turning occasionally, until crisp (about 3 minutes).

Transfer the bacon to a paper towel-lined plate to drain.

Add the thinly sliced yellow onions to the pot, sprinkle in the dark brown sugar, and sauté until the onions are a deep caramel brown (about 35 minutes).

Stir in the minced garlic and cook for another minute.

Transfer the onion mixture to a plate and set aside.

On another plate, combine the all-purpose flour, 1 teaspoon of salt, and 1/2 teaspoon of fresh ground pepper.

Dredge the round steak chunks in the seasoned flour, shaking off any excess.

Melt the remaining 2 tablespoons of unsalted butter with the olive oil in the pot over medium heat.

Working in batches, sear the steak, turning occasionally, until browned on all sides (about 10 minutes per batch).

Transfer the seared steak to a plate.

Pour in the dark beer and stir to scrape up any browned bits from the pot bottom (deglaze).

Bring the beer to a boil.

Return the caramelized onion mixture and the seared steak to the pot.

Cover the pot and cook over low heat until the meat is very tender (about 2 hours).

Divide the stew among shallow bowls and serve hot.