In a large cast-iron skillet or Dutch oven over medium heat, warm 1 tbsp olive oil.
Add the onion, carrot, celery, sweet potato and a big pinch of salt. Stir, cover and cook for 10 - 15 minutes, or until vegetables are fork tender. Stir occassionaly.
Sprinkle in the rosemary and thyme and stir to coat vegetables.
Stir in the dijon mustard.
Sprinkle in the flour and cook for about 1 minute.
Pour in the broth and cream and bring to a boil. Reduce heat to medium low and allow broth to reduce and thicken.
Add the peas, stir and allow to cook for 1 minute.
Pour vegetable mixture into a 9 x 13 casserole dish.
Preheat oven to 400.
In a food processor, add the flour, baking powder, baking soda and butter and process until butter is the size of a pea.
Pour flour mixture into a bowl and, using a wooden spoon, stir in milk and buttermilk until the dough just comes together. Mix in the rosemary.
Pour dough out onto lightly floured parchment paper. Bring it together with your hands with just a few pats and then flatten it out until it's 1-inch thick.
Using a biscuit cutter or back of a drinking glass, cut out biscuits and set on top of vegetable mix. Gather scraps and continue until dough is used up.
Brush top of biscuits with egg wash.
Bake casserole for about 20 - 25 minutes, or until biscuits are golden brown and casserole is bubbling. Serve and enjoy.
