2 tablespoons unsalted butter
2 tablespoons all-purpose flour
Preheat the pressure cooker (by pressing brown/sauté mode).
Add the olive oil and sear the beef cubes on one side (about 5 minutes). Add rosemary, onions, celery, red wine, stock, salt, and pepper. Mix the contents of the pressure cooker well. Sprinkle the mushrooms and carrots on top of the stew mixture.
Close the lid and pressure-cook for 15 minutes at high pressure. When time is up, open the pressure cooker with natural release (turn off the pressure cooker and wait for pressure to come down naturally, about 15 to 20 minutes).
In the meantime, in a small pan melt the butter and drizzle with flour. Mix into a paste and let it cook until the butter begins to make bubbles in the flour.
Remove the lid, tilting it away from you. Add about 6 tablespoons of the cooking liquid from the pressure cooker into the little pan with the flour paste and mix well to loosen the paste. Then, pour the mixture back into the pressure cooker base and mix well.
Bring the contents of the pressure cooker to a boil (by pressing brown/sauté mode) and let it simmer until thickened (about 5 minutes).