Ingredients (Serves 4–6):
- 1½ lbs (700g) potatoes, peeled and thinly sliced
- 2 tablespoons butter
- 1 small onion, finely chopped
- 2 cloves garlic, minced
- 2 tablespoons all-purpose flour
- 1½ cups milk (warm)
- ½ cup sour cream or heavy cream
- 1½ cups shredded cheddar cheese (or cheese blend), divided
- 1 can (5–7 oz / 150–200g) tuna in water or oil, drained and flaked
- Salt and pepper, to taste
- 1 teaspoon Dijon mustard (optional, for flavor)
- ½ cup breadcrumbs or crushed crackers (for topping)
- 1 tablespoon olive oil or melted butter (to mix with crumbs)