Steps:

• Combine 1 1/2 cups sugar, lukewarm water, and 1 cup lukewarm milk in a very large bowl. Add yeast and let stand until yeast softens and begins to form a creamy foam, about 10 minutes.
• Add 2/3 cup melted butter and 2 eggs to the bowl with the yeast mixture and mix well. Add 7 cups flour, 1 cup at a time and mix in; when dough comes together, start kneading until elastic but still sticky. Cover the bowl and let rise for 1 hour in a warm place.
• Divide dough into 36 equal pieces; cover and let buns rise for 1 hour more.
• While buns rise, beat 1 cup sugar and 1/2 cup butter together in a bowl. Add egg yolks, 4 tablespoons milk, and baking soda. Combine 2 cups flour and baking powder in a separate bowl; add to the sugar-egg yolk mixture. Refrigerate cookie topping at least 1 hour.
• Flatten 1 bun in your palm; place a spoonful of red bean paste inside. Squeeze edges together to cover filling and roll bun back into a ball. Let filled buns rise again, 30 minutes to 1 hour.
• Preheat the oven to 350 degrees F (175 degrees C).
• Divide cookie topping into 36 equal balls. Flatten the balls and use a knife to make shallow hash mark lines resembling pineapple skin on each. Place 1 topping on each bun and place them on a baking sheet.
• Bake in the preheated oven until golden, 15 to 20 minutes.