Melt butter and olive oil in a large pot over medium heat
Add onion and cook until soft and translucent, about 4–5 minutes
Stir in garlic and cook for 30 seconds until fragrant
Sprinkle flour over onions and stir constantly for 1–2 minutes
Slowly whisk in chicken broth until smooth
Add cooked chicken, milk, and heavy cream
Season with salt, pepper, and optional poultry seasoning
Bring to a gentle simmer and cook for 10 minutes
In a bowl, mix dumpling flour, baking powder, and salt
Stir in milk and melted butter until just combined
Drop spoonfuls of dumpling dough into simmering broth
Cover the pot, reduce heat to low, and cook for 12–15 minutes
Gently stir once dumplings are cooked through
Taste and adjust seasoning if needed