I learned this trick at a restaurant! Why didn't I know this method before?

I learned this trick at a restaurant! Why didn't I know this method before? 👉ATTENTION !! Turn on subtitles yourself. They are translated by Google and available in each language. Ingredients: 150ml lukewarm Water 150ml lukewarm Milk 2 Tbsp (24g) Sugar 1 Tbsp (9g) dry instant Yeast 2 Tbsp (30ml) Vegetable oil 1 Egg 650g Flour 1 tsp (4g) Salt 2 Tbsp Butter 2 Potatoes 2 Tbsp Butter 100g Cheese 1 Egg yolk Sesame seeds 200 ml lukewarm Milk 1.5 tbsp Sugar 1 Tbsp(9g) instant Yeast 2 eggs 1\4 cup(50ml) Vegetable oil 550g flour 1 tsp Salt 3 tbsp Butter For layering 4 Tbsp butter Ricotta Cheddar cheese Spinach 1 tsp Salt