Prepare the veggies by dicing or slicing into similar sized pieces. Set aside. Measure ingredients for the dumplings and set aside (separately).
Using a heavy bottomed braising pan or Dutch oven, melt 1 tbsp butter over medium-high heat. Once melted, add the onions, carrots, and celery. Saute 6-7 minutes or until the onions are translucent and fragrant. Stir in the garlic, thyme, and MSG and cook 1 minute more, then transfer the veggie mixture to a bowl.
Melt the remaining butter in the same pan and reduce to low or medium heat. Stir in the flour until it’s fully absorbed. Once smooth, cook for 7-10 minutes to form a blonde or light roux.
Pour in the turkey broth, whisking to scrape the frond from the bottom of the pan. Raise the heat back to medium-high to bring to a low simmer. Once thickened, stir in the vinegar, turkey, and peas.
Meanwhile, mix the AP flour, chives, garlic, salt, baking powder, and baking soda for the dumplings. Whisk the egg with the buttermilk, then pour it in and mix with the dry ingredients to form a loose, shaggy dough (do not overwork). Use a tablespoon to scoop the dough onto the turkey mixture, leaving space between to allow for expansion as they cook. Repeat with the remaining dough.
Reduce heat to low, cover, and cook 15-20 minutes or until the dumplings are fully baked. Garnish with additional chopped chives (option), season with salt and pepper to taste. Serve hot.