Heat olive oil in a large Dutch oven over medium-high heat. Season chicken with salt and pepper, then cook until golden brown, about 5-6 minutes. Remove and set aside.

In the same pot, melt butter and add onions, carrots, and celery. Cook until vegetables soften, about 5 minutes. Add garlic and cook for another minute.

Sprinkle flour over vegetables and stir constantly for 2 minutes to cook out the raw flour taste.

Gradually pour in chicken broth while stirring continuously to prevent lumps. Add thyme and bring to a simmer.

Return chicken to the pot and stir in heavy cream. Reduce heat to medium-low and let simmer for 10 minutes.

Meanwhile, prepare the dumplings: Whisk together flour, baking powder, and salt. Cut in cold butter using a pastry cutter until mixture resembles coarse crumbs. Stir in cold milk until just combined.

Drop dumpling dough by spoonfuls onto the simmering stew. Cover and cook for 15-18 minutes, or until dumplings are cooked through.