Stuffed mushrooms can be both a party appetizer and an everyday treat if you use the largest mushrooms you can find to make the process go quickly and if you solve the problem of excess water. When buying mushrooms, choose those with tightly closed caps and even coloring. Your choices for mushrooms include large, flavorful portobellos, brown, 2-inch cremini mushrooms or white, button mushrooms that reach up to 3 inches wide.
Why Water is a Problem
Lots of water on your baking sheet is a safety problem with the risk of spilling scalding water, not to mention the annoyance of having to clean up any spills. If those were the only problems, you could probably take precautions to resolve them. But the excess water also causes the mushroom caps to steam rather than roast, and that takes away some of the concentrated flavors that roasting normally provides.
Some fillings are watery by nature and contribute to the problem of excess water. If you use chopped mushrooms or tomatoes as part of the filling, be sure to cook those ingredients first in a skillet until they are fairly dry before using them in the mushroom caps. Another alternative is to omit any watering ingredients in the filling. Stick with a mixture of cream cheese and goat cheese topped with fresh bread crumbs instead.
Cooking unstuffed mushrooms prior to baking or broiling solves the problem of excess water. To cook the mushrooms in a skillet, oil a preheated pan and lay the mushrooms in a single layer, cap side down, for about 10 minutes until they release their water. Or, roast the unstuffed mushrooms, tossed with oil, salt and pepper, in a 450-degree Fahrenheit oven for 10 minutes on each side. Set the mushrooms on a wire rack placed in a baking sheet to keep them above the liquid.
Because they are so large and contain up to 90 percent of their weight in water, portobello mushrooms present special problems. Begin by removing the large, woody stem with your fingers and the dark gills of the mushroom by scraping them out with a spoon, leaving plenty of room for the stuffing. Pre-cook portobellos either in a skillet or in the oven, but first, cut three or four slits into the caps to help the water release quickly.