Trim off excess fat from the steak and cut into bite sized pieces. Remove excess moisture with paper towels.
In a heavy bottom skillet or dutch oven, heat 2 tablespoons butter to foaming and place mushrooms, cut side down in the pan. Do not flip or move the mushrooms for about five minutes, or until they start to sweat and brown on the underside.
4 Tablespoon Butter, 8 ounces fresh baby bella mushrooms
Flip the mushrooms and sear on the second side. Add additional butter, if needed.
Stir in the shallots and cook for a minute longer.
3 Tablespoon shallots
Move the cooked mushrooms and shallots to a slow cooker.
Add 2-4 more tablespoons to the skillet or dutch oven warm over moderately high heat.
Sear the beef, a few pieces at a time, for 2-3 minutes on each side to brown the exterior but keep the interior is still medium in doneness.
2 ½ pounds steak
move the beef to a slow cooker.
Deglaze the pan with the wine, stock and Worcestershire sauce scraping up the bits of yummy stuck on beef, onion and mushroom bits.
½ Cup dry white wine, 1 Cup beef stock, 1 Tablespoon Worcestershire
Add the wine stock and Worcestershire along with the bits to the slow cooker.Add the thyme.
1 Teaspoon Thyme
Cook on low for 6-8 hours.
Once cooked, remove as much of the liquid as possible and return it to the pan you used to sear the beef and turn the heat to medium high.
While the sauce is reducing, whisk together the cornstarch mixture with a splash or so of heavy cream or milk.
2 teaspoons cornstarch blended with 1 tablespoon of the cream, 1 Cup Heavy Cream
After the sauce has reduced, add the heavy cream/corn starch mixture to the pan, whisking to incorporate. It will be thick.
Bring to a simmer for one minute. This will cook out the corn starch taste and activate the thickening properties of the corn starch.
Pour in the remaining heavy cream and whisk to combine. Bring to a simmer.
Add the stroganoff sauce back to the slow cooker. Add cooked noodles.
Season with salt and pepper.
salt and pepper
Serve over cooked noodles, if desired.