Despite nearly 20 years of Chinese rule, Great Britain’s colonial flavors still reign in Hong Kong kitchens. Western ritual and Asian taste collide during afternoon tea when billowy, warm pineapple buns are sliced in half and sandwiched with a fat pat of butter. The buns, made with the Chinese tangzhong roux method and English custard powder, contain no pineapple whatsoever, but are so named for their iconic crosshatch crust and yellow crumb.
Whisk the water and 1 1/2 tablespoons flour together in a small saucepan, then place over low to medium heat. Continue whisking for about one minute or until the slurry thickens to the consistency of yogurt. Allow the roux to cool slightly before adding it to the dough mixture below.
In a medium bowl, gently whisk together the warm roux, cream, milk, and egg white and set aside. Place all the remaining dry ingredients in the bowl of an electric stand mixer fitted with a dough hook. Turn the machine on medium speed and slowly pour in the liquid ingredients. When a cohesive dough forms, begin to add the soften butter a little bit at a time, making sure each pat fully incorporates into the dough before adding more. Let the machine run for another five minutes until the dough is nice and soft and no longer sticks to the bowl. Cover the dough with plastic wrap and leave it to rise until doubled in size, about two hours.
To make the crust:
In the bowl of an electric mixer fitted with a paddle attachment, cream the butter until pale and fluffy. Add the egg yolk and continue to mix until fully incorporated. Add the remaining dry ingredients and mix just until the dough comes together. Use your hands to press the dough into a ball, wrap with plastic wrap, and chill in the refrigerator for at least an hour.
Line two sheet trays with parchment paper an set aside. Punch the air out of the proofed dough and place on a clean surface. If it's super sticky, you can add a scant sprinkling of flour, but I find this dough easier to work with sans flour. Use a bench scraper or a chefs' knife to cut the dough into 10 equal portions. Rolls each portion into a ball shape, placing five buns on each sheet tray. Cover the buns with plastic wrap and allow them to rice for another half hour.
Use this time to preheat your oven to 400º F and to prepare the crust.
Remove the crust dough from the refrigerator and cut into 10 portions. Roll each portion into a ball then place between two sheets of parchment paper and press it into a flat disk with the bottom of a measuring cup. The circles should be about 3 1/2-inches in diameter.
Place one crust round atop each proofed bun, using your hand to gently shape the crust to the dough. Don't worry that the crust doesn't cover the whole thing...that's just the way it's supposed to be! Whisk together the egg and the water and brush the crust and dough with the egg wash.
Bake for 15-20 minutes until golden brown.
Let the buns cool until they are easy to handle, slice in half with a serrated knife, and sandwich with a questionably thick slab of butter.