Prepare the crust: Place the disk of pie crust dough onto a well floured surface. Use a floured rolling pin to roll the dough out to around 1/8 of an inch thick. Using an empty ramekin or soup bowl as a guide, use a sharp knife or dough cutter to cut 4 circles of dough, roughly 1/2 inch wider than the tops of your ramekins. Place the circles of dough on a parchment or silicone lined baking sheet and then place in the fridge.
Preheat oven to 400 degrees.
Heat a large skillet over medium-high heat. Add the butter and once melted, add in the diced onion, celery, sliced carrots, and minced garlic. Sauté the veggies until the onion and is translucent and the veggies have started to become tender.
Sprinkle the flour over the veggies and stir until well combined.
Pour in the chicken broth, half and half, lemon juice, thyme, salt, and pepper. Turn the heat to medium-low and let the sauce simmer until it has thickened a bit.
Next, turn off the heat and stir in the chicken and the frozen peas until well combined.
Divide the filling evenly among 4 large oven safe ramekins or soup bowls and set aside.
Top each ramekin with a circle of cold pie crust, gently pressing the edges it to ensure it is sealed. Cut four 1/2 inch slits into the top of each crust and then brush with egg wash.
Bake the pot pies for 20-25 minutes at 400 degrees until the crust is golden brown. Top with flaky sea salt and fresh thyme.