• Step 1: Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish with butter or non-stick cooking spray.
• Step 2: In a large skillet, melt 2 tablespoons of butter over medium heat. Add the diced onion and minced garlic, and sauté until the onion is translucent, about 5 minutes.
• Step 3: Add the diced chicken to the skillet and cook, stirring occasionally, until the chicken is lightly browned, about 8-10 minutes.
• Step 4: Sprinkle the all-purpose flour over the chicken mixture and stir to coat. Cook for 2-3 minutes, allowing the flour to coat the chicken and vegetables.
• Step 5: Gradually pour in the chicken broth and milk, stirring constantly to prevent lumps from forming. Bring the mixture to a simmer and cook until thickened, about 5 minutes.
• Step 6: Stir in the frozen mixed vegetables, dried thyme, dried rosemary, salt, and black pepper. Taste and adjust seasoning as needed.
• Step 7: Pour the chicken and vegetable mixture into the prepared baking dish, spreading it out evenly.
• Step 8: In a medium bowl, whisk together the 2 cups of all-purpose flour, baking powder, baking soda, and salt. Cut in the chilled, cubed butter using a pastry blender or two forks until the mixture resembles coarse crumbs.
• Step 9: Stir in the buttermilk until just combined, being careful not to overmix. Drop the cobbler dough by large spoonfuls onto the top of the chicken and vegetable mixture, covering the surface as evenly as possible.
• Step 10: Bake the casserole for 30-35 minutes, or until the cobbler topping is golden brown and the filling is bubbly around the edges.
• Step 11: Allow the casserole to cool for 10-15 minutes before serving. Enjoy!