Potato Gratin

**Potato GratinIngredients** - 4 large russet potatoes, washed and thinly sliced (skins on) - 2 shallots, finely diced - 5 cloves garlic, minced - 3 sprigs thyme, leaves picked - 50g butter - 50g plain flour - 1 glass white wine (about 150ml) - 200g Gruyere cheese, grated - 500ml whole milk - Salt and freshly ground black pepper, to taste - Optional: Fresh chives, chopped (for garnish) **Instruct