Heat butter in a large 5-6 quart saucepan or Dutch oven over medium-high heat. Add diced onions and cook for 3-4 minutes, stirring occasionally, until the onions are translucent and slightly softened.

Sprinkle flour over the butter and onions, stirring constantly to create a roux. Cook this mixture for 2-3 minutes, stirring constantly, until it just begins to turn a light golden color.

Pour in the condensed chicken broth while whisking to prevent lumps, then add the heavy cream. Stir until smooth and bring to a gentle boil, stirring frequently to prevent scorching. This should take about 5-7 minutes.

Once boiling, reduce heat slightly and add the well-drained peas and carrots, shredded chicken, salt, pepper, onion powder, and sage. Stir until well combined.

Cut each refrigerated biscuit into four equal pieces. Gently add the biscuit pieces to the pot, stirring carefully to coat with sauce without breaking them apart. Reduce heat to medium-low and cover with lid.

Simmer for 20 minutes, lifting the lid to stir gently every 5 minutes to prevent sticking. The biscuit dough will puff up and cook through. After 20 minutes, the dumplings should be cooked through (no longer doughy in center when torn open) and the sauce should be thick enough to coat the back of a spoon.