Preheat oven to 400 degrees F. Grease and lightly dust a 10-inch fluted tube pan or an 11-cup ring mold with cornmeal.
In a large mixer bowl, combine biscuit mix, milk, eggs and butter. Beat with an electric mixer on low speed until well combined. Beat on high speed for 1 minute, scraping bowl constantly. With back of spoon, spread 2/3 of the dough on the bottom and up the sides of the prepared pan to within 1 1/2 inches of the top; reserve remaining dough. Layer mushroom, pepperoni, pizza sauce and 1 1/2 cups of the cheese over the dough in pan. Spread reserved dough over the top of cheese layer. Bake for 30 minutes or until golden.
Let pizza stand for 10 minutes on a warm rack. Use a knife to loosen sides of pizza, turn out onto ovenproof serving plate. Top with remaining cheese. Return pizza to oven for 1 to 2 minutes to melt cheese. Serve warm.
Makes 6 to 8 servings.