Preheat a sous vide bath to 190° F.
Wash the little potatoes and trim any imperfections, leaving the skin on.
Add the potatoes, 2 tbsps unsalted butter, 1 tbsp olive oil, 1 tbsp minced garlic, 2 sprigs rosemary, 1 tsp salt, and 1 tsp pepper to a sous vide bag. Vacuum-seal the bag in a flat layer.
Sous vide the sealed bag at 190° F for 60 minutes.
When the sous vide cook is complete, preheat the broiler to high. Remove the potatoes from the bag, transfer them to a baking sheet, and broil on high about 5 minutes until the skins start to crisp. Sprinkle with 1 sprig fresh thyme to garnish.