First I slice the mushrooms into even pieces and cut the steak into 1-inch cubes. I pat both dry: the steak especially must be dry to sear properly. Then I season steak cubes with salt, pepper, and smoked paprika so they carry flavor.
I heat up butter and olive oil in my skillet over medium-high heat until shimmering. Then I add the steak bites in a single layer (don’t crowd the pan) and sear about 3-4 minutes per side until nicely browned. Once the steak is roughly where I like it, I push them to the side.
In the same pan (with the steak juices), I add more butter if needed, throw in the mushrooms, and sauté until they release moisture and turn golden. Then I reduce heat to medium, add minced garlic, cook it just ~30 seconds until fragrant (but not burnt), toss everything together so mushrooms and steak are coated in garlic butter. Finish with chopped parsley if using, and serve hot.