Slow-Cooker Vegetable Pot Pie

Heat 2 teaspoons of the oil in a large nonstick skillet over medium-high. Add the mushrooms, potatoes, leek, and carrots; cook, stirring often, 5 minutes. Add the garlic; cook, stirring often, 1 minute. Sprinkle the vegetables with 1/4 teaspoon of the salt. Coat a 6-quart slow cooker with cooking spray. Transfer the vegetable mixture to the slow cooker.

Heat the remaining 2 tablespoons oil in the skillet over medium-high; whisk in 3 tablespoons of the all-purpose flour. Cook 1 minute, whisking constantly. Reduce the heat to medium, and gradually whisk in the stock. Cook, whisking constantly, until thickened and bubbly, about 3 minutes. Stir in the thyme, pepper, and 7/8 teaspoon of the salt. Pour the sauce into the slow cooker; stir gently to combine. Cover; cook on LOW until the vegetables are tender, 3 to 4 hours.

Whisk together the pastry flour, baking powder, and remaining 1/2 cup all-purpose flour and 1/4 teaspoon salt. Cut in the chilled butter with a pastry blender or 2 knives until the mixture resembles a coarse meal. Stir in the cheese and chives. Add the milk, stirring just until moistened.

Add the peas and half-and-half to the slow cooker; stir to combine. Increase the slow cooker heat to HIGH. Drop the biscuits onto the filling in 6 equal mounds (see Tip). Cover and cook on HIGH until the biscuits are cooked through, about 1 hour. Uncover; let stand 5 minutes before serving. Garnish with the additional chopped chives, if desired.