In a mixing bowl, whip 4 oz of softened cream cheese for about 1 minute using an electric hand mixer. Then add in 1/4 cup mayonnaise, 6 oz lump crab meat, 2 sliced green onions, 1 Tbsp chopped parsley, 2 pressed garlic cloves, 1/4 tsp salt, 1/8 tsp black pepper, and 1/3 cup grated Parmesan cheese. Then set it aside.
Wipe about 20 large mushrooms with a damp paper towel to remove any debris. Then use a small spoon or melon baller to remove stems and spoon out the insides of the mushroom and discard.
Line a baking sheet with parchment paper and place the mushrooms on top. Now use a medium-sized cookie scoop to spoon and fill each mushroom cap with the creamy crab mixture.
Now thoroughly combine the panko bread crumbs with the melted butter and sprinkle on top of the filled mushrooms. Preheat the oven to 375 degrees Fahrenheit and bake for about 18 minutes, then broil for about 2 minutes to get the tops golden and crispy.
Notes
Soften the cream cheese- It's much easier to thoroughly combine the filling when the cream cheese is softened. This avoids unwanted clumps of pure cream cheese in the mushrooms.
Clean off the mushrooms caps- Because mushrooms grow down in the dirt, they can gather a lot of debris and mud. Wipe them well to get them clean and ready to eat.
Use melted butter with the Panko- Don't try to sprinkle Panko alone on the mushrooms as it will mostly slide off. Adding butter helps it adhere in a thick layer to the tops.
Broil at the end- To get that perfect, crusty top, broil for 2 minutes at the end of cooking to send heat directly on top of the Crab Stuffed Mushrooms. This makes them nice and crispy.