- Preheat the oven to 400 deg. F.
- Heat the olive oil in a medium frying pan over high heat. Add the mushrooms and a pinch of salt and sauté, stirring frequently, until they are browned and all their liquid has evaporated, 4 to 5 minutes. Transfer to a bowl and let cool in the refrigerator.
- Combine the flour, baking powder, and the remaining 1Ž4 teaspoon salt in the bowl of a food processor. Add the butter cubes and pulse 5 to 8 times, until the butter is just incorporated and the mixture resembles little peas.
- Transfer the dough to a bowl and, using a wooden spoon, mix in the milk and two-thirds of the gruyere, the cooled mushrooms, and the scallions until just incorporated.
- Divide the dough into 6 equal portions and form each into a loosely packed ball. Place on a rimmed baking sheet, leaving 1 inch between each biscuit.
- Brush each biscuit with the egg wash and sprinkle the remaining provolone over the tops. Bake for 20 to 22 minutes, rotating the pan halfway through. Serve warm or at room temperature.
Pairs with Clos du Bois North Coast Chardonnay.