
This custardy steamed egg breakfast sandwich is made with harissa mayonnaise, breakfast sausage and cheddar cheese but can be customized with your breakfast favorites.
Heat oven to 300ºF (150ºC). Set a rack in the middle of the oven and coat an 8” x 8” (20cm x 20cm) pan with butter. Line the pan with parchment paper and butter once more.
Add the eggs to a medium mixing bowl and whisk well until the eggs fall like ribbons from the whisk. Add the half and half, chives and season with salt. Pour the egg mixture into the greased pan.
Set the pan with the eggs into a larger 9”x11” (23cm x 29cm) baking pan. Boil water and pour into the larger bottom pan then carefully transfer to the oven. Bake until the eggs are just set, about 30 minutes.
Use towels or oven mitts to transfer the dish out of the water bath and onto a cooling rack and let cool slightly, about 5 minutes.
Carefully run a knife around the edges of the pan and lift out of the pan onto a cutting board. Cut the eggs into 4 equal squares.
Divide the breakfast sausage into 4 equal portions and shape them into patties just larger than the buns. Heat a large cast iron pan over medium-high heat. Add the sausage patties and press down with a metal spatula so they are thin and smashed. Cook until golden brown, about 2 minutes. Flip using a spatula and continue to cook until just cooked through and browned on the other side, about an additional 2 minutes.
In a small bowl stir together the mayonnaise and harissa until combined.
Turn the oven to broil on high. Top each egg piece with a slice of cheese and transfer to one side of a baking sheet. Arrange the buns on the other side of the baking sheet. Broil until the cheese has melted and the buns are toasted, about 1 minute.
Spread harissa mayonnaise on the bottom bun. Top with a sausage patty followed by the egg with the melted cheese. Close each sandwich and serve hot.