In a medium bowl, season the beef with salt and pepper and toss to coat.
Add ¼ cup (30 g) of flour, and toss the beef cubes until they are fully coated.
In a large pan over medium-high heat, heat the canola oil until it shimmers. Place about half of the beef cubes in the pan. Sear the beef on one side until it develops a deep brown crust, 3-5 minutes. Then flip and sear on the other side for 3-5 minutes. Then, stir the beef until evenly browned on all sides. Remove the beef from the pan. Repeat with the remaining meat.
Melt the butter in the leftover meat drippings.
Add the onion, season with salt and pepper, and cook until the onions are soft and slightly golden, about 5 minutes.
Add the sliced mushrooms and cook until deeply browned and tender, about 10 minutes.
Add the cognac and scrape the brown bits, releasing them from the bottom of the pan. Cook and stir until the cognac is fully incorporated, about 2 minutes.
Sprinkle the remaining ¼ cup (30 g) flour into the pan and stir to coat the the caramelized veggies.
Add the beef broth and stir it into the flour and vegetables. Bring the liquid to a boil, then reduce to low heat and simmer for 10 minutes. The sauce should be thick enough to coat the back of a spoon.
Once the sauce is thickened, turn off the heat. Put two scoops of hot gravy into a bowl with the sour cream. Mix the two together to slightly warm, or temper, the sour cream. Then add the sour cream mixture to the rest of the gravy and stir it in until fully combined.
Sprinkle the stroganoff with chopped parsley and serve with buttered egg noodles, rice, or potatoes.