Preheat the oven
Before you start assembling the ingredients, make sure that the oven is preheated at 350 degrees Fahrenheit.
Prepare the mushrooms
Slice the mushroom stems from the caps and place them aside. Make sure that the caps are wiped with a dry towel. Take the stems and chop them down with a sharp knife.
Heat butter in pan
Take a dry pan and melt some butter in it. Make sure you keep the stove on medium heat, so that the ingredients cook nicely.
Add the ingredients in the pan
After chopping the onions, add them to the pan and wait until they get golden brown. Now, add the garlic, stems, sauce, pepper, and sherry to the pan.
Add breadcrumbs and cook on high heat
After the mushroom stems get tender, add the breadcrumbs to the pan and increase the heat to high. Continue cooking the mixture for a few minutes until there is no moisture left. Once it is dry, you can add cheese to it.
Stuff the mixture into mushroom caps
After the breadcrumb mixture cools down to some extent, stuff it into the mushroom caps and bake for 15 minutes.
It is now ready to be served.