Think of this four-ingredient side as super-deluxe garlic bread. It's a fun way for the whole family to dig into some nutty pesto swirled together with gooey mozzarella cheese.
Preheat oven to 350 degrees. Cut into Italian demi-loaves (or 1 large loaf) at 1-inch intervals, taking care not to slice all the way through. Spread 1 teaspoon pesto between each slice. Stuff with thinly sliced low-moisture mozzarella and thinly sliced Taleggio. Wrap in parchment-lined foil and bake on a rimmed baking sheet until bread is crisp and cheese is melted, about 25 minutes. Serve immediately.