4cupsbaby spinach5 to 6 ounces, 110 to 140g, rinsed and spun very dry
¼cupshredded smoked gouda30g
goodbalsamic vinegarfor serving
Set an oven rack 5 inches (12 cm) from the heat source. Flip on the broiler.
Whisk the eggs, cream, ½ teaspoon salt, and ¼ teaspoon pepper in a medium bowl. Set aside.
Swirl the oil along the bottom and up the sides of a 9 ½-inch (24cm) cast-iron or ovenproof, nonstick skillet. (You may use a pastry brush.) Set the skillet over medium-low heat, add the shallot, and sauté, stirring occasionally, until soft and translucent, about 5 minutes. Add the spinach, one handful at a time, turning with tongs so it wilts. Crank the heat and sauté for about 5 minutes, until the spinach weeps and its moisture then evaporates, tossing a few times. (You want it relatively dry.) Lower the heat again.
Add the egg mixture, cheese, and tomatoes and cook until the frittata is three-quarters set, about 5 minutes, tilting the skillet now and again so the runny eggs slide toward the edges.
Broil until puffy and browned, 3 to 5 minutes, watching carefully. Let cool for 5 minutes. Serve wedges warm or at room temperature, with balsamic vinegar for dribbling.