Step 1

Remove stems from each mushroom and wipe the cap clean with a damp paper towel. Scrape the gills out of the cap with a spoon.

Step 2

Cut mushroom caps into ¼ inch slices.

Step 3

Melt butter and oil in a large heavy skillet, preferably cast-iron over medium-high heat until hot and the mixture is foamy. Add garlic and shallot, and sauté for 30 seconds, stirring constantly. Add mushrooms, thyme, salt, and pepper, and cook, stirring often, until the mushrooms have released their juices and their juices have evaporated and then the mushrooms have started to caramelize and brown, 5 to 8 minutes.

Step 4

Stir in sherry and cook stirring until the sherry has evaporated about 30 seconds. Remove from the heat and stir in tarragon or parsley, if using. Serve hot, warm, or at room temperature.