Remove the steak from the refrigerator and allow it to come to room temperature (about 30 minutes). Turn on the Crockpot to Low.
Tenderize the steak with the side of a bowl or the edge of a plate. Or of course a traditional meat tenderizer will work.
Generously season flour with salt and pepper and dredge steak in flour mixture.
Melt 2 tablespoons butter or cooking oil in skillet or dutch oven over medium-high heat. Once the pan is hot, add the steak and sear both sides until browned (about 3 minutes per side).
Remove the steak and set aside. Add another tablespoon of butter and scrape up the browned bits from the bottom of the pan. Add diced onion and saute until softened. Add garlic and saute until fragrant.
Add the tomatoes, onion, garlic, garlic salt, celery salt and pepper into the Crock pot and stir to combine. Place the steak in the crockpot and cover with the tomato mixture. Cover and cook on low for 7 hours.
Serve with mashed potatoes, mashed cauliflower, polenta or over a baked potato.
If you don't have 7 hours, you can cook on high for 4 hours but for best flavor and texture, I highly recommend cooking beef on slow and low.