Preheat the oven to 400 degrees.
Make the biscuits by combining the flour, baking powder, salt, and baking soda together in a bowl. Add the diced butter and cut with a pastry cutter until crumbly.
Add the sharp white cheddar and chives along with the buttermilk; mix until just combined. Don't over mix.
Dump the dough out on a floured surface and roll into a rectangle (you may have to sprinkle the dough with flour if it's too sticky).
Fold the dough in half over itself, and roll into another rectangle. Repeat two more times.
On the last time, roll the dough out 1/4 inch thick.
Use a 2 1/2 inch biscuit cutter and cut 8 biscuits. If needed, re-roll scraps to make final biscuit.
Place the biscuits in the freezer while you make the pot pie.
Make the pot pie filling by heating the butter over medium high heat in a large cast iron skillet.
Add the onions, mushrooms, carrots, and potatoes then cook, stirring often, for 10 minutes.
Add the minced garlic and cook, stirring constantly, for 1 minute.
Add the flour to the vegetables and gently mix evenly, cooking the flour for a minute or two.
Slowly add the chicken broth and milk, stirring often. Bring mixture to a boil then simmer for 3-4 minutes, allowing it to thicken a bit.
Add the chicken and frozen peas; mix well. Taste and season with sea salt and freshly cracked pepper, to taste.
Add the biscuits to the top of the pot pie filling.
Whisk together the egg with the water.
Brush each biscuit top with a bit of the egg.
Place into the oven and bake for 17-20 minutes, or until the biscuits are golden brown.
Remove from the oven and allow to cool for a few minutes before serving. Enjoy.