Yukon Gold Gratin with Turnip and Parsnip | Heinen's Grocery Store

Ingredients

• 1 tablespoon unsalted butter
• 1 teaspoon fresh thyme, minced
• 2 teaspoons Dijon mustard
• 2 cups heavy cream, plus more if necessary
• 1/2 cup milk, plus more if necessary
• 1 teaspoon salt
• Freshly ground black pepper
• 2-lbs Yukon Gold potatoes, peeled, halved and very thinly sliced
• 1/2-lb parsnips, peeled and very thinly sliced
• 4-oz turnip, peeled, halved and very thinly sliced
• 8-oz Gruyère cheese, grated