Place the chicken breasts or thighs directly into the bottom of the 6-quart crock pot.

In a separate bowl, whisk together the two cans of cream of chicken soup, the chicken broth, dried minced onion, thyme, pepper, and salt.

Pour the soup and broth mixture over the chicken in the slow cooker. Ensure the chicken is mostly submerged.

Cover the slow cooker and cook on LOW for 6 to 8 hours or on HIGH for 3 to 4 hours. The chicken should be very tender and easily shredded.

Once the chicken is fully cooked, carefully remove the chicken pieces and place them on a cutting board.

Using two forks, shred the chicken and then return it to the crock pot mixture. If using, stir in the heavy cream and frozen mixed vegetables now.

Turn the crock pot setting up to HIGH to bring the liquid mixture to a simmer while preparing the dumplings.

In a medium bowl, combine the 2 cups of Bisquick baking mix with the 2/3 cup of milk. Stir just until a wet, sticky batter forms. Do not overmix.

Using a tablespoon or a small cookie scoop, drop spoonfuls of the dumpling batter directly onto the surface of the simmering chicken mixture in the crock pot. Space them slightly apart, as they will expand.

Ensure the dumplings are resting on top of the liquid rather than sinking to the bottom. If the liquid isn't simmering, wait a few minutes before dropping the batter.

Cover the crock pot tightly and continue to cook the dumplings on the HIGH setting for 30 to 45 minutes. Do not lift the lid during this cooking time, as the trapped steam is essential for cooking the dumplings completely.

The dumplings are done when they are puffy, firm to the touch, and cooked through (no doughy centers). Serve the Chicken & Dumplings hot.