Preheat broiler. Arrange tomatoes, cut sides up, on a rimmed, aluminum foil-lined baking sheet. Broil 4 inches from heat 5 minutes. Remove from oven; let cool slightly.
Whisk together eggs, half-and-half, salt, and pepper in a large mixing bowl.
Heat butter in an ovenproof 10-inch skillet over medium heat. Add spinach; cook about 30 seconds or until spinach barely begins to wilt. Pour in egg mixture. Sprinkle with fontina, dill, and 4 tablespoons basil; stir gently with a fork.
Arrange tomatoes, cut sides down, over egg mixture; press down gently with the back of a spatula. Crumble goat cheese evenly over the frittata. Reduce heat to medium-low, and cook about 6 minutes or until frittata is almost set but still runny on top.
Broil 6 inches from heat 2 minutes or until completely set and golden brown. Remove from oven, and let stand 2 to 3 minutes. Sprinkle with remaining 2 tablespoons basil. Cut into wedges and serve.