Spiced Tomato Gratin

INGREDIENTS

• 1 teaspoon whole cumin seeds
• 2 teaspoons curry powder
• 1/2 teaspoon red pepper flakes
• 1/4 cup extra-virgin olive oil
• 6 cups thinly sliced yellow onions (about 2 pounds / 32 oz / 910 g)
• 1 tablespoon unsalted butter
• 1 1/4 pounds / 20 ounces / 570 g Yukon Gold potatoes
• 1/2 cup / 120 ml heavy cream
• 2 pounds / 32 oz / 910 g ripe tomatoes
• a small handful of basil leaves, slivered
• sea salt and freshly ground pepper