It is easiest to roast the garlic immediately before making this recipe. If you preroasted it, turn on your oven and preheat to 400°F.
Heat the oil or butter in a large skillet. Add the mushrooms, sherry and thyme. Cook, stirring frequently, until mushrooms change color and are softer, but not significantly shrunken. Remove from heat.
In a bowl, combine the roasted garlic, cream cheese and goat cheese together (preferably when the garlic is still warm to melt everything together). Resist the temptation to use a food processor; mix by hand to maintain the chunks of roasted garlic. Spread mixture on top of the pizza crust.
Evenly distribute the mushrooms on top of the garlic-cheese spread.