Preheat oven to 400°F (200°C). In a large oven-safe skillet or Dutch oven, melt 1/4 cup of butter over medium heat. Add onion, carrots, and celery and cook until softened, about 5-7 minutes. Stir in minced garlic and cook for 1 minute more.

Sprinkle the flour over the vegetables and cook, stirring, for 1 minute. Gradually whisk in the chicken broth and heavy cream until smooth. Bring to a simmer and cook until thickened, about 3-5 minutes.

Stir in the shredded chicken, frozen peas, corn, thyme, salt, and pepper. Remove from heat.

In a large bowl, whisk together the flour, baking powder, sugar, and salt. Cut in the cold cubed butter using a pastry blender or your fingers until the mixture resembles coarse crumbs. Stir in the cheddar cheese.

Pour in the cold buttermilk and stir with a fork until just combined. Do not overmix.

Drop large spoonfuls of the biscuit dough over the chicken filling in the skillet.

Bake for 20-25 minutes, or until the filling is bubbly and the biscuits are golden brown.

While baking, combine the 2 tbsp melted butter and garlic powder. Brush the garlic butter over the hot biscuits as soon as they come out of the oven. Let rest for a few minutes before serving.