Steps
- Preheat the oven to 400°F / 205°C. Arrange 12 slices of thin-cut bacon on a foil-lined rimmed baking sheet. Bake for 15-20 minutes, until crisp; drain on paper towels.
- Mix ½ cup of mayonnaise, 2 tablespoons of sour cream, and 2 teaspoons of yellow mustard.
- Spread 1½ tablespoons of softened unsalted butter thinly over both sides of 8 slices of sourdough bread, cut ½in / 1cm thick.
- Toast the bread in a dry skillet over medium-high heat until golden on both sides. Spread the sauce over one side of each slice.
- Layer half the bread with 4 green lettuce leaves, 2 large thickly sliced ripe tomatoes, and the bacon. Season with salt and pepper; close with the remaining bread and cut in half.