French Onion Skillet Casserole - Better Than Bouillon

Ingredients

• 2 tbsp butter, divided
• 1 lb lean ground beef
• 2 onions, thinly sliced
• 2 tbsp Better Than Bouillon Organic Roasted Beef Base
• 2 tbsp Dijon mustard
• 1 tbsp finely chopped fresh thyme
• 5 oz baby spinach
• 3 tbsp canola oil, divided
• 1/2 pkg (30 oz) frozen shredded hash browns (about 4 cups)
• 2 cups shredded Gruyère cheese