Pineapple Bun (菠蘿包)

Ingredients

• 4 tbsp butter
• 2 tsp milk
• 1 egg yolk
• 1/2 teaspoon vanilla extract
• 2/3 sugar
• 1 cup all-purpose flour
• 1/2 teaspoon baking powder
• 1/2 teaspoon baking soda
• salt to taste
• 1 1/2 cup milk
• 1/3 cup sugar
• 2 1/4 tsp (1 packet) yeast
• 1 large egg
• 2 cups bread flour
• 1 3/4 cups all-purpose flour
• 1 tsp salt
• 3 tbsp butter, softened
• 2 egg yolks
• 1/2 tsp sugar