Prepare the spinach: If using fresh, place it in a large pot with only the water clinging to the leaves.
Cover and cook over low heat until just wilted.
Drain in a colander, let cool, then squeeze out as much water as possible with your hands.
Mince finely. If using frozen, simply thaw and squeeze out all excess moisture.
Create the custard: Preheat your oven to 375°F / 190°C.
In a large bowl, beat the eggs well.
Stir in the cream, basil, salt, pepper, and the prepared minced spinach.
Mix until thoroughly combined.
Prepare the water bath: Generously butter a 1½-quart ring mold, loaf pan, or soufflé dish.
Pour in the spinach mixture.
Place this dish inside a larger baking dish and pour enough hot water into the larger dish to come halfway up the sides of your mold.
Bake the custard: Bake for 20 to 30 minutes, or until a knife inserted into the center comes out clean.
Let the ring rest in its mold for 10 minutes before unmolding.
Make the sauce: While the spinach ring is resting, increase the oven temperature to 450°F / 230°C.
In a small bowl, combine the tomato purée, cream, salt, and pepper.
Mix well.
Unmold and finish: Carefully run a knife around the edge of the mold and invert it onto an attractive, shallow oven-safe dish.
Pour the tomato cream sauce evenly over the spinach ring and sprinkle with Parmesan cheese.
Final bake: Bake for an additional 15 minutes, or until the sauce is bubbling and the top is golden brown.
Serve immediately.
When buying fresh spinach, look for vibrant green leaves free of yellow spots. If using loose spinach, buy a full two pounds, as removing the stems significantly reduces the weight.
