Frittata Sandwich with Potatoes, Olives and Peppers Recipe
Make the garlic-caper mayonnaise: Place egg yolk, garlic, and lemon juice in a blender or mini-food processor. With the machine running slowly add ½-cup oil in a thin stream until thick and well emulsified. Scrape the mayonnaise into a small bowl or jar. Stir in the capers. Cover and refrigerate up to 4 days.
Make the sautéed sweet peppers: Heat 2 tablespoons oil in a large nonstick skillet set over medium heat. Add sweet peppers; season with salt and pepper. Cook, stirring occasionally, until peppers are just tender, about 10 minutes.
Scrape the sweet peppers onto a plate to cool. They can be made up to two days in advance. Cover and refrigerate until ready to use. Bring to room temperature before use.
Make the frittata: In a medium bowl combine eggs and milk (or cream); season generously with salt and pepper. Beat lightly until blended. Set aside.
In a medium saucepan, cover the potatoes with water by about 1-inch; season generously with salt. Bring to a boil, then lower the heat to a simmer. Cook until tender, about 10 minutes. Drain and set aside.
Preheat the oven to 350 degrees Fahrenheit.
Stir the the olives to the egg mixture; set aside.
Heat remaining ¼-cup oil in a 10-inch cast iron or other nonstick ovenproof skillet set over medium heat. Add onions; cook, stirring often, until soft and just beginning to color, about 8 minutes. Add the potatoes to the skillet, gently spread them evenly across the bottom.
Increase the heat to medium-high. Pour the egg and olive mixture over the onions and potatoes, gently shaking the pan to evenly distribute mixture. Cook the frittata, without stirring, until its edges begin to set, about 3 minutes. Transfer skillet to oven. Bake frittata until golden brown and center is set, 25-30 minutes.
Once cooked, cool frittata a few minutes then slide or flip it onto a cutting board. Cool completely, then cut into two rectangular slabs, sized to fit the ciabatta rolls. Save scraps as a snack.
Assemble the sandwiches: Split the ciabatta rolls in half and remove a little of the inside crumb creating a shallow well in the center of each of the top halves. Arrange tops and bottoms, cut side up, in a single layer on a rimmed baking sheet. Brush the top surface of each ciabatta lightly with olive oil. Place baking sheet into heated oven. Bake until bread is lightly golden on the edges; about 12 minutes. Take baking sheet out of the oven and let ciabatta cool slightly before assembling sandwich.
When ready to serve, spread both interior sides of each ciabatta roll with some garlic-caper mayo. Top the bottom halves with a generous helping of sautéed sweet peppers and place a frittata slab on top of each. Generously fill the indentations of the top rolls with baby kale. Put the sandwiches together, cut in half and serve within a couple of hours.