How to Make It
Working over a strainer set over a bowl, seed the tomatoes, reserving the juices. Coarsely chop the tomatoes.
In a blender or mini-processor, pulse the tomatoes, jalapeño, cilantro and cumin until finely chopped but not pureed. Transfer to a bowl and stir in 2 tablespoons of the reserved tomato juices. Stir in the salt.
Preheat the broiler. In a 10-inch omelet pan, preferably nonstick, melt the butter until the foam subsides. In a medium bowl, combine the eggs and milk and season with salt and pepper. Add the eggs to the pan and cook over high heat without stirring until the edges set. Lower the heat to moderate and lift the sides of the omelet, tilting the skillet to let the uncooked eggs spread underneath. Cook until the bottom is golden and the top is still slightly runny, about 3 minutes.
Spoon 1/2 cup of the pico de gallo on top of the eggs and sprinkle with the cheese and scallions. Set the pan under the broiler and broil until the top is set and the cheese is melted. Slide the frittata onto a large plate and cut into wedges. Serve the remaining pico de gallo alongside.