Thaw your spinach and artichokes overnight in the fridge or in the microwave. Then squeeze them like you mean it — place in a clean kitchen towel and wring until no more liquid comes out. Set aside.

Preheat oven to 400°F (205°C) and line a large rimmed baking sheet with parchment. Remove stems from mushrooms and scrape out every bit of the dark gills with a spoon (this prevents grey filling).

Brush caps lightly with olive oil, place gill-side DOWN on the sheet, and bake exactly 10 minutes. You’ll see a surprising amount of liquid — this step is non-negotiable!

While they bake, make the dip filling: beat softened cream cheese, mayo, and sour cream until completely smooth (no lumps!).

Fold in 1 cup mozzarella, ½ cup Parmesan, all the Gruyère/pecorino, minced garlic, salt, pepper, and red pepper flakes. Then gently mix in the squeezed artichokes and spinach until evenly distributed. Taste — it should make you weak in the knees.

Remove mushrooms from oven. Carefully flip them, pour off all collected liquid, and pat the insides completely dry with paper towels. Your mushroom cups are now perfectly prepped!

Place a scant tablespoon of the dip filling in each cap and spread to the edges (this creates a base layer).

Pile another generous 1½–2 tablespoons on top, mounding high — really overfill them, they shrink! Press lightly so it stays put.

Mix the remaining ½ cup mozzarella + ¼ cup Parmesan and sprinkle heavily over each mushroom. Bake 14 minutes until filling is hot and edges are golden, then switch to BROIL (high) for 1.5–2 minutes until the tops are blistered and bubbling (stand there and watch!).

Rest 10 full minutes (they’re nuclear inside), then transfer to a platter with a spatula. Optional: sprinkle with extra Parmesan or fresh parsley. Serve with zero shame as people fight over the last one.