Preheat oven to 425ºF.
TO PREPARE BISCUITS:.
To make biscuit topping, sift remaining 2 cups flour with baking powder, baking soda, and remaining 1 teaspoons salt.
Using two forks, your fingers or a pastry cutter, cur in unsalted butter to form a coarse meal, working quickly to keep the butter from warming up and melting into the dough.
Stir in cheese and sage.
In a separate bowl, whisk together egg and buttermilk and add to the flour mixture, stirring gently until a shaggy dough forms.
Lightly flour a counter, a rolling pin, and your hands.
Divide dough into 2 balls.
Roll out first ball to a 1/4-in. thickness, then use a 2 1/2-in. biscuit cutter or glass to cut into rounds, scraping and rerolling dough as needed.
Repeat with second ball.
Place 3 rounds of dough on each potpie, overlapping as necessary (bake unused rounds on their own as biscuits).
PREPARE CHICKEN & VEGETABLES;.
In a medium saucepan over high heat, bring chicken stock to a boil.
Add carrots, potatoes, and celery.
Lower heat to medium and cook until vegetables are tender, 5-7 minutes.
Drain vegetables, reserving stock; set both aside separately.
In a large Dutch oven melt salted butter over medium heat.
Add onion, cook until golden, 6-8 minutes.
Add mushrooms; cook 5 more minutes.
Add fresh thyme and 5 tablespoons flour and cook 2 minutes.
Slowly add milk, whisking constantly, until combined, then add stock and cook, stirring often, until mixture thickens, 8-10 minutes.
Season with nutmeg, 1 teaspoons salt, black pepper to taste, & red pepper flakes, if using.
Add parsley, chicken, cooked vegetables, and peas and divide filling evenly among 6 or 7 ovenproof containers, leaving the top 1/4 inches unfilled.
FINAL ASSEMBLY & BAKING:.
Place 3 rounds of dough on each potpie, overlapping as necessary (bake unused rounds on their own as biscuits).
Brush dough with egg wash, put potpies on a cookie sheet lined with aluminum foil, and bake until crust is golden brown and filling is bubbling, 17 to 22 minutes.
Serve with sliced tomatoes & onions with a light vinaigrette dressing and a nice wine.
Enjoy!