3/4cupred onion (about 1 large red onion), thinly sliced
4ouncescream cheese, cut into small cubes
4ouncessmoked salmon, cut into large strips
2Roma tomatoes, cut into thin slices
Preheat the oven to 400 degrees (F). Carefully crack eggs into a medium-large bowl; whisk eggs until well beaten and frothy; about 2 minutes by hand. Whisk in heavy cream, milk, scallions, dill, black pepper, and salt; mix well to combine; set aside. In a large ovenproof skillet, melt the butter over medium heat. Once it's completely melted add egg mixture to skillet. Quickly layer the red onion, cream cheese, smoked salmon, tomatoes, and capers on top of the eggs. Cook for 4 minutes over medium-heat without stirring or moving the eggs in any way. At this point carefully transfer the skillet to the oven.
Bake until the top is golden brown and the frittata is set; about 35 minutes. Cool for 5 minutes, then cut and serve warm.