Roasted Beef Tenderloin with French Onions

Ingredients

• 3 lb. whole, trimmed beef tenderloin
• ½ cup olive oil, divided
• 1 kosher salt, to taste
• 1 tbsp. granulated garlic
• 3 tbsp. cracked black pepper, divided
• 1 fresh thyme leaves, for garnish
• 1 fresh chopped parsley, for garnish
• 2 lbs. thinly sliced onions
• 4 tbsp. butter
• 1 tsp. chopped, fresh thyme
• 1 tsp. chopped, fresh rosemary
• 1 bay leaf
• ¼ cup rice wine vinegar
• 2⁄3 cup mayonnaise
• 2⁄3 cup sour cream
• 3 oz. prepared horseradish
• ½ tsp. lemon, zest and juice