Heat large skillet (preferably cast-iron) over medium heat.
Add bacon to pan and cook until fairly crispy and browned. Remove bacon and set aside, leaving 2 Tbsp fat in the pan and setting remaining bacon fat aside.
Season flour with kosher salt and freshly ground black pepper. Toss beef in seasoned flour and sear in pan for 1 minute per side until browned on all sides. Remove beef from pan and set aside.
Add garlic, onions and carrots to pan and sauté until bright and onions are translucent.
Add red wine and fresh thyme to pan and simmer until wine is reduced by half.
Add bacon and beef back to pan and simmer 1 more minute.
Add beef stock to pan with 2 Tbsp flour. Whisk to combine and simmer on low heat for 15 minutes.
Preheat separate small skillet over medium heat. Add 1 Tbsp bacon fat and saute pearl onions until lightly browned. Set aside.
Add 2 Tbsp butter to small skillet and sauté mushrooms until browned. Set aside.
Once stew has simmered for 15 minutes, remove thyme sprigs. Add mushrooms/onion mixture and 1 stick cold butter. Whisk to combine. Add parsley, and season with salt and pepper to taste.