Grease a 13" x 9" baking pan or casserole
Heat a large, heavy bottom pot over medium heat. Add the olive oil, celery, onions, and carrots. Saute for 5 minutes until carrots are just tender. Add the flour and stir thoroughly so no dry spots remain. Whisking constantly, add the chicken stock to the flour and vegetables. Bring to a simmer stirring constantly until thickened. Add the cream and continue simmering and stirring for a couple of minutes. Check and adjust the seasoning with salt and pepper. Add the potatoes, cooked chicken, peas, and thyme. Scrape the filling into the casserole or baking pan and set aside to cool slightly while you make the biscuits.
In the bowl of a food processor add all of the dry ingredients and pulse. Add the chilled butter and pulse a few times to incorporate and create small pea sized lumps of butter. Add the butter olive oil to the buttermilk and pour over the dry ingredients. Pulse a few more times until a loose, moist dough forms.
Preheat the oven to 350 F.
Roll out the dough to 1" thickness and cut out biscuits 2" in diameter. Place the biscuits on top of the pot pie filling about 1" apart. Brush with additional buttermilk and bake for 25 minutes until biscuits are fluffy and golden.