In a large skillet, heat 3 Tbsp. vegetable oil. Stir in 3 chopped small red onions, 2 chopped cloves garlic, 1/2 Tbsp. chopped ginger, 1/2 tsp. thyme leaves and 1/8 tsp. allspice; season with salt and pepper. Cook, stirring, for 10 minutes. Stir in 1 tsp. brown sugar; let cool. Stir in 1 cup sour cream.