Japanese Souffle Pancakes - The Garnished Palate

Ingredients

• 3 large egg whites + 1 yolk
• 1/4 tsp. cream of tartar
• 1 1/2 c. all purpose flour
• 2 tsp. baking powder
• 1/2 tsp. kosher salt
• 1 1/4 c. whole milk
• 6 tbsp. unsalted butter, melted & cooled, divided
• 3/4 tsp. pure vanilla extract OR substitute orange blossom water
• Nonstick cooking spray
• 1/2 c. brown sugar
• 1/4 c. maple syrup
• 1 tbsp. bourbon