Prepare the smoker for barbecuing, bringing the temperature to 200°F to 220°F.
Stem the mushrooms and hollow out the caps. Chop the stems and trimmings and reserve.
Warm the butter and oil in a skillet. Add the mushroom caps and sauté over medium-low heat for 2 to 3 minutes, turning frequently. Remove the partially cooked mushroom caps from the pan an