BEEF BURGERS WITH GARLIC MAYO & ONION RINGS

1 large sweet potato • About 100ml sunflower oil for frying, plus 2 tbsp extra for roasting • ¼ tsp hot smoked paprika • 4 garlic cloves, skin left on • 2 brioche buns, halved • 2 Gourmet Burger Kitchen Beef Burgers • ½ onion, cut into 1cm slices • 1 tbsp whole milk • 3 tbsp plain flour, seasoned • 2 tbsp light mayonnaise • 2 tbsp tomato chutney • handful lettuce leaves • 2-3 tomatoes, sliced