Finely chop the onion. Add chopped onions, oil, salt, and pepper to the bowl of a large slow cooker, cover, and turn of high while you prepare the rest of the veggies.
Chop the potatoes into ½-inch dice. Make sure they are all fairly uniform in size so they cook at about the same rate.
Peel and chop carrots into ¼-inch thick slices.
Add chopped potatoes, carrots, and broth to the slow cooker. Cover and turn to low. Cook on low for 6 to 8 hours.
After filling has cooked for 6-8 hours, and veggies are tender.
In a microwave safe bowl, melt butter in the microwave, about 30 seconds. Stir the ½ cup of flour into the butter, and mix the 1 ½ cups milk, dried thyme, garlic powder, and wine into flour. Stir with a whisk until most of the lumps have dissolved. Don’t worry if you have some left, they will disappear into the pot pie.
Stir the milk-flour mixture into the veggies in the slow cooker.
If making the dumpling biscuits start making them in here.
Stir the thawed peas into the pot pie filling, (remove one of the biscuits from the top if necessary to get at the filling). Taste the filling for salt and pepper.
Serve the pot pie while hot. Garnish with additional fresh thyme if desired.