1/2 cup (120 milliliters) shredded old cheddar, for topping
Preheat oven to 400F (220C).
To make the frittata, fry bacon in a medium-sized, heavy frying pan until crispy. Drain frying pan of excess bacon fat. Add diced onions and cook over medium heat until softened. Evenly spread onions and bacon over the bottom of the pan.
In a small bowl, whisk eggs with milk, salt and pepper. Pour over bacon and onions. Arrange diced tomato evenly over the top of the eggs. Place frying pan in the oven and cook until eggs have set and the edges are golden brown, about 15-20 minutes.
To make the butter leaf salad, tear butter leaf lettuce leaves into bite-sized pieces. Whisk mayonnaise, bacon fat, lemon juice, sugar, salt and pepper in a salad bowl. Toss torn lettuce leaves and diced tomatoes into bowl with dressing and toss to coat evenly.
Top frittata with butter leaf salad. Season with extra salt and pepper. Sprinkle with shredded old cheddar.
Watch the video below for some ideas with what to do with your leftover ingredients!