Grease a half sheet pan very well with non-stick spray (or line with parchment paper. Heat the oven to 300°F. Crack all 12 eggs in a mixing bowl, add salt and pepper and the splash of cream, then whisk until well combined. Stir in the bacon and chives.
Pour the mixture into the prepared pan. Sprinkle with cheese evenly, if using. Bake until the eggs are just set, about 15 minutes. Transfer to a cutting board and cut into squares. Top on toasts.