Preheat oven to 400°F (204°C) and line a baking sheet with foil or parchment paper. Slice the sourdough bread into ½" thick slices.
Mix the butter, garlic and chives in a small bowl. Salt to taste. Spread the garlic herb butter evenly onto each slice of bread and sprinkle both cheeses on top.
Bake for 15-20 minutes or until the cheese is melted and has started to turn golden brown on top. Serve immediately.
Notes
Store leftovers in fridge wrapped in foil for up to 2 days. Reheat in oven at 350°F (176°C) until cheese is melted and bread is heated through.