Mexican buns aka coffee cookie buns aka rotiboy buns
The Chinese like soft and fluffy white breads. The whiter, the better. It might explain why something called Hong Kong flour exists. The HK flour is bleached and low in protein so that the resulting bread is super white and super soft. I don't really mind if my Chinese breads turn out white or not. So I just use what I have on hand which is Central Milling's Artisan Bakers Craft, a 10.5% protein, organic, malted, unbleached flour. The results are definitely more off-white than white. Soft and fluffy is easy. Enrichments such as butter, egg and milk will do the trick. Using a tangzhong aka water roux helps with the softness and keeping quality.
This bun is a purely Asian creation. It doesn't seem to have anything to do with Mexico although buns with a cookie-like topping are reminiscent of conchas. I don't know who invented it first and I have no idea why the Chinese like topping breads with a cookie batter, but it's pure genius. The cookie melds with the bread dough and creates a thin, crispy, cookie-ish layer. Depending on the ingredient ratios in the cookie batter, the layer can be fused with the bread and cannot be peeled off. Or if the cookie batter is stiffer, the baked layer can be peeled or flaked off the bread and eaten separately which is the way I did it as a child when eating boh loh bao aka pineapple buns (which have no pineapple in it at all).
I used instant espresso powder in my cookie topping, but instant coffee powder can be used instead. You can leave out the coffee and have a plain vanilla topping. I used a tangzhong milk loaf for my buns. They turned out super soft, fluffy and shreddable. The topping was crisp on day one, but softened considerably by day two.
I left a few without topping. The topping weighs down the bun a bit so the topped ones spread out instead of up.
The bottom of the bun.
Bakers' percentages for the bun dough
100% flour*, 75% whole milk*, 10% sugar, 12.5% egg, 1% instant dry yeast, 1.5% salt, 10% butter
[* 5% of the total flour was used in the tangzhong. TZ ratio was 1:5 flour to milk.]
Bun dough recipe
To make the tangzhong: In a saucepan whisk 20 g AP flour into 100 g whole milk until it's pretty smooth. Cook over medium heat, whisking constantly, until the mixture reaches 149F/65C. It should be pudding like. Allow the tangzhong to cool before using it in the dough.
380 g AP flour
200 g whole milk, 85-90F
50 g egg
4 g instant dry yeast (SAF red)
6 g salt
40 g unsalted butter, softened
all of the tangzhong
In a KA stand mixer, mix everything except the butter on speed 1 for 3 minutes.
Add the butter and mix on speed 2 until all the butter is incorporated, about 2 -3 minutes.
Bulk ferment at room temp until doubled, about 1 hour.
Scale each bun at 55 grams. (I got 15 buns.)
Proof on sheet pans at room temp for 30-45 minutes.
Pipe cookie topping onto each proofed bun.
Bake buns at 375F for about 15 mins or until golden brown. Best served warm.
Coffee cookie topping
50g unsalted butter, softened
50g granulated sugar
50g egg, lightly beaten
70g AP flour
1 tsp instant espresso powder
1 tsp water
1/2 tsp pure vanilla extract
Dissolve the espresso powder in the warm water and mix in vanilla extract. Set aside.
Beat the butter and sugar until light and fluffy.
Beat in the egg until well combined.
Beat in the espresso mixture.
Add the flour and mix until just incorporated.
Transfer topping to a pastry bag fitted with a round pastry tip.
Store in the refrigerator until needed. (Can be made 2 day in advance.)
Allow the topping to soften a bit at room temp for about 5 or 10 minutes before piping it onto the proofed buns.