Preheat the oven to 450 degrees F.
In a large bowl combine the butter, olive oil, rosemary, and salt. Add the potatoes to the bowl and toss to coat.
Lay the potatoes flat, spaced out in a single layer on a rimmed baking sheet.
Place in the center of the oven and bake for 15 minutes.
Flip each potato over. Sprinkle the garlic and shallots around the pan and slowly pour the chicken stock onto the baking sheet.
Cook for 15 minutes more.
Serve with some of the cooking liquid.
