Scatter the finely diced yellow onion across the bottom of a greased 6-quart slow cooker pot.

Lay the cubed chicken thighs uniformly over the bed of onions. Pro Tip: Swapping traditional chicken breast for chicken thighs is a total game-changer for the slow cooker. Thighs contain more natural intramuscular fat and collagen, which allows them to stay incredibly juicy and tender over hours of cooking instead of turning stringy and chalky.

In a separate medium bowl, whisk together the cream of chicken soup, cream of celery soup, poultry seasoning, black pepper, and fresh parsley until completely smooth.

Pour the thick soup mixture evenly over the chicken, then pour the chicken broth around the sides of the pot. Cover with the lid and cook on High for 4 hours.

Once the 4-hour mark hits, remove the lid. Stir the thawed frozen mixed vegetables directly into the hot chicken gravy.

Open the can of refrigerated biscuits. Use the palm of your hand to flatten each dough round slightly on a clean surface, then slice them into thin strips or small bite-sized squares using a pizza cutter. Drop the biscuit pieces one by one onto the surface of the chicken stew. Use the back of a spoon to gently press them down just enough to moisten the dough with the warm liquid—do not stir them in completely.

The High-Steam Cook: Immediately replace the lid and turn the slow cooker heat setting to High for 60 to 90 minutes. Crucial: Keep the lid tightly sealed and resist the urge to peek. The biscuits cook and expand purely through the hot steam trapped inside the crockpot. Lifting the lid lets that heat escape instantly, which will cause your dumplings to deflate and turn into heavy, gummy dough balls instead of light, pillowy clouds. Serve hot once the dumpling centers are entirely cooked through and no longer shiny.