Cut 1 large round from each bread slice with a biscuit or cookie cutter. Cut bacon into small pieces with kitchen shears and sauté in an 8-inch skillet until crisp. Remove bacon to paper towels; pour bacon grease into bowl and do not wipe out skillet.
Add a small amount of olive oil as needed to the pan and toast the bread rounds on each side until golden. Set aside.
Add the remaining bacon grease to the skillet and heat, then add sherry vinegar, whisking until it begins to emulsify. Season with pepper to taste.
Arrange bread slices on plates topping each with a tomato slice, crumbled bacon, basil and repeat. Sprinkle with blue cheese and drizzle dressing over stacks. Serve immediately. 4 servings.