Preheat oven to 350°.
Whisk together eggs and cream in a large bowl for about 45 seconds. Stir in basil and cheese and season with salt and pepper.
Heat oil in an ovenproof skillet over medium heat. Finely chop onion and mince garlic and then cook, stirring, for about 3 minutes.
Slice tomatoes crosswise into 1/4 inch thick slices.
Pour egg into hot pan and immediately pull egg from the sides into the middle a bit. Arrange tomato slices, staggering colors, and the basil leaves. Add to the oven and bake for 15-20 minutes, or until the egg is set in the middle. Serve at any temperature.