INGREDIENTS
2 tbsp
extra-virgin olive oil
1
small yellow onion, peeled, halved, and sliced thinly
1 tsp
red pepper flakes
2 28 ounce cans
whole tomatoes
1 1/2 cups
water
1/4 cup
loosely packed fresh basil leaves, plus more for garnish
About 2 teaspoons kosher salt, or to taste
About 1 tablespoon balsamic vinegar, or to taste
4
(1/2-inch-thick) slices rustic white bread
2 tbsp
unsalted butter, melted
4 oz
Gruyère cheese, grated
Neutral oil, such as grapeseed or canola
Freshly ground black pepper