Sandwich Keju Panggang terbaik saya

Bahan-bahan (1 porsi)

• 2 slices sourdough bread (, sliced 1.3–1.5cm thick (0.5 - 0.6") - Note 1)
• 30 g / 2 tbsp SALTED butter (, for spreading on bread (or unsalted + pinch of salt))
• 1/3 cup (heaped) vintage cheddar cheese or gruyere, (freshly grated (or other melting cheese of choice) - Note 2)
• 30 g / 1/3 cup mozzarella, ( freshly grated - Note 2)