In a medium bowl, whisk eggs, heavy cream, milk, salt, and pepper. Set aside.
Preheat oven to 400 degrees. Place cherry tomatoes on a baking sheet and bake for 15 minutes. Let them cool.
Heat a large skillet over medium to medium-low heat, add the olive oil. Saute onion, stirring occasionally, for 5 minutes, or until the onion is soft and mostly transparent.
Add as much spinach as will fit and stir. Cook the spinach until it’s just wilted. Transfer everything to a plate to cool.
Reduce oven temperature to 350 degrees and lightly grease a 9-inch quiche plate or deep-dish pie plate.
Spoon spinach and onion mixture into prepared plate. Sprinkle cheese evenly over the top. Pour the egg mixture over the spinach mixture in the prepared pie plate. Top with roast tomatoes.
Bake until the quiche is just set in the center, approximately 35 minutes, although this can vary based on the depth of your pie plate. Look for the center to set and not jiggle. Cool on a rack before serving.
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