Slow Cooker Scalloped Sweet Potatoes - Better Than Bouillon

Ingredients

• 2 Tbsp unsalted butter, softened
• 1 lb yellow potatoes, peeled and thinly sliced
• 1 lb sweet potatoes, peeled and thinly sliced
• 1 large onion, thinly sliced
• 1 Tbsp fresh thyme, finely chopped
• .75 cup 35% heavy cream
• 2 Tbsp Better Than Bouillon Seasoned Vegetable Base
• 1 Tbsp Dijon mustard
• 1 cup shredded Gruyère cheese
• .33 cup grated Parmesan cheese
• 2 Tbsp finely chopped fresh chives