Preheat oven to 375°F. Lightly spray 4 shallow, ovenproof dishes, each about 3-4” in diameter. Divide the cherry tomatoes among the dishes, spreading them out, and sprinkle each with the chives and 4 tbsp of cheese. Break eggs into a bowl and whisk them with the egg whites, then gradually whisk in flour until smooth. Add sour cream, then gradually whisk in the milk to make a thin, smooth batter. Season lightly with pepper. Pour batter over tomatoes, dividing it evenly among the dishes. Sprinkle with the remaining cheese and an extra grinding of pepper. Bake until set, puffed and lightly golden, 30-35 minutes. Serves 4.