Begin by preheating the oven to 350°. At this point, you can also lightly grease a foil-lined cookie sheet, on which you will eventually set your mushrooms.
Clean the mushrooms by wiping them with a wet paper towel, and remove the stems to hollow them out. The filling will eventually be placed inside the cavity, so it is helpful to thoroughly remove the stem.
In a food processor, or by hand, finely chop your garlic into small pieces. Melt butter over medium heat in a pan, and add garlic to it. Cook until lightly browned, stirring regularly. When the garlic is lightly browned, remove it from the heat and set aside.
Using your food processor, reduce the slices of white bread to small pieces, and transfer to a bowl. Add the two tablespoons of sour cream, one teaspoon of salt, and browned garlic and mix together until well combined. Spoon the mixture into the hollowed mushrooms
Lay mushrooms on your cookie sheet and drizzle with olive oil. Bake for 20 minutes at 350°.
