Venison Tenderloin with Berry Sauce and Creamy Potatoes

Name: Venison Tenderloin with Berry Sauce and Creamy Potatoes
Ingredients: 3 medium Yukon gold potatoes; Kosher salt; 3 tablespoons butter, room temperature; 1 teaspoon ground nutmeg; 1 tablespoon heavy cream, plus more if needed; Salt and freshly ground white pepper; 2 venison tenderloins; Salt and freshly ground black pepper; 3 tablespoons grapeseed oil; 1 cup red wine; 1 cup demi glace; 1 small red onion, halved; 2 sprigs fresh thyme; 1 sprig fresh rosemary; 1 tablespoon juniper berries; 1 teaspoon sugar; 1/3 cup blueberries; 2 tablespoons butter