Wash and dry the mushrooms.

Cut off the ends of the stems without separating them from the caps.

Slice the mushrooms 1/8-inch-thick lengthwise.

Sprinkle the sliced mushrooms with seasoning salt, fines herbes, and dry mustard.

Melt butter in a skillet over medium heat.

Add the mushrooms to the skillet and brown them, adding more butter if necessary to keep them moist.

When the mushrooms are nearly done, add red wine vinegar.

Reheat the mushrooms with the vinegar.

Serve hot.