Heat bacon grease in a skillet on medium high heat.
Pat cubed beef dry with paper towels, season with salt and pepper and dust lightly with flour. Arrange the beef around the pan and brown on all sides. Remove and set aside.
Reduce heat to medium and add the mushrooms, onions and garlic to the pan; sauté until the aromatics (onions and garlic) are soft and the mushrooms have released much of their liquid and started to brown.
Add the sherry to de-glaze the pan and cook for about 1 minute, then add the beef broth, cream of mushroom soup and the browned beef cubes.
Simmer for about 20 minutes, add the heavy whipping cream, and simmer another 10 minutes. Add the sour cream and stir until heated throughout.
Remove from heat and stir in the sour cream.
Add additional salt and pepper to taste if desired.
Notes
Getting the oil extremely hot before adding the beef helps it to get browned and develop a crust on the outside. This crust adds flavor and also helps the meat become more tender and juicy on the inside.
Don't add the sour cream until you have removed the pan from the heat. Sour cream will curdle if it boils. We want to just stir it into the already warm sauce for a nice and creamy texture.
You can make this with ground beef as well if that's all you have on hand. Just brown the ground beef at the same time you would have cooked the tenderloin.
You really want a tender cut of beef for this recipe. I typically use tri-tip, but tenderloin or ribeye would work great as well.
If you don't have sherry, you can leave it out. However, I find it adds a great flavor to the stroganoff and recommend using it if you can.
To make ahead: Follow recipe instructions up to the point where sour cream is added. Store stroganoff sauce in a container in the fridge overnight or up to 3 days. to reheat, place sauce in a skillet and heat over medium heat until it starts to simmer. Add additional broth to thin the sauce if necessary. Once sauce is bubbling and has reached desired consistency, add the sour cream. Stir until heated through then remove from heat and serve with egg noodles.
To freeze: Let the stroganoff cool then place in an airtight container. Store in the freezer for up to 3 months. Thaw in the fridge overnight then heat on the stove top or in the microwave. Add additional beef broth if the sauce is too thick, until desired consistency is reached.