Preheat large skillet to medium high. Add butter and olive oil to pan. When the butter is melted, add the mushrooms in a single layer.

Sprinkle tops of the mushrooms with ¼ teaspoon kosher salt and cook without disturbing for 3 minutes to form a nice sear.

Flip mushrooms and cook with minimal stirring for an additional 2-3 minutes until browned on the other side.

Reduce heat to medium low. Add garlic and another splash of olive oil if it's looking dry, along with half the spinach. Cover for 30 seconds to wilt the greens.

Stir, add the other half of the spinach, and cover for another 30 seconds.

Add remaining ¼ teaspoon salt and a squeeze of fresh lemon juice. Stir to combine and serve immediately.