Pineapple Buns (Bolo Bao)

Before you start

Bolo bao contain no pineapple. The name comes from the golden, cracked top, which looks a little like pineapple skin. Each bun is a soft milk bread with a disc of sweet, buttery cookie dough laid over it; in the oven the topping spreads, cracks and turns crisp while the bread underneath stays feathery. In Hong Kong they are often split warm and filled with a thick slab of cold butter, known as bolo yau.

This version uses a tangzhong, a cooked flour-and-milk paste that lets the dough hold more moisture, so the buns stay soft for days. The topping is the part to watch. It should be soft enough to roll between plastic but firm enough to hold an edge, and it goes on just before baking, after the buns have fully proofed. Too much leavening in the topping makes it spread off the sides; too little gives a smooth top with no crackle.

Ingredients

• Tangzhong20 g (2½ tbsp) bread flour
• 100 ml (⅓ cup + 4 tsp) whole milk
• Dough280 g (2¼ cups) bread flour
• 40 g (3 tbsp) granulated sugar
• 5 g (1½ tsp) instant yeast
• ¾ tsp fine salt
• 1 large (about 50 g) egg
• 80 ml (⅓ cup) whole milk — lukewarm
• 30 g (2 tbsp) unsalted butter — soft
• Topping50 g (3½ tbsp) unsalted butter — soft
• 60 g (½ cup) powdered sugar
• 1 large egg yolk
• 1 tbsp whole milk powder — optional; adds a milky flavor
• 100 g (¾ cup + 1 tbsp) cake flour or all-purpose flour
• ½ tsp baking powder
• ⅛ tsp baking soda
• 1 large egg yolk — beaten with 1 tsp water, for glazing

Method

1. Whisk the 20 g flour and 100 ml milk in a small saucepan over medium-low heat. Stir constantly for 2 to 3 minutes, until it thickens into a pudding-like paste that leaves trails, about 65°C (150°F). Scrape into a bowl, cover the surface and cool for 15 minutes.
2. Put the 280 g flour, sugar, yeast and salt in the mixer bowl. Add the tangzhong, egg and lukewarm milk and mix on low until combined. Knead on medium for 6 minutes, add the soft butter and knead 6 to 8 minutes more, until smooth and stretchy.
3. Cover and let rise at about 26°C (78°F) for 60 to 75 minutes, until doubled.
4. Make the topping: beat the soft butter and powdered sugar until creamy, then beat in the yolk. Add the milk powder, flour, baking powder and baking soda and stir just until a soft dough forms. Wrap and refrigerate it while the buns proof.
5. Divide the dough into 8 pieces of about 75 g, shape into tight balls and space them on the lined sheets. Cover and proof for about 45 minutes, until puffy and nearly doubled. Heat the oven to 180°C (350°F).
6. Divide the topping into 8 pieces of about 30 g. Roll each between plastic wrap into an 8 cm (3 in) disc about 4 mm thick.
7. Lightly brush each proofed bun with egg yolk glaze and lay a disc on top without pressing hard. Brush the topping with glaze too. Score a shallow crosshatch with a knife if you want a more defined pattern.
8. Bake one sheet at a time for 15 to 18 minutes, until the tops are deep golden and cracked. Cool on a rack for at least 15 minutes; the crust crisps as it cools.

Tips for success

• Chill the topping until it is firm but still pliable. If it cracks when rolled, let it sit at room temperature for 5 minutes.
• Rest the topped buns for no more than 5 minutes before baking. Longer, and the warm buns soften the topping so it slips.
• For bolo yau, split a warm bun and tuck in a 1 cm slice of cold salted butter.

Substitutions

Cake flour (topping)

All-purpose flour gives a slightly harder, less sandy crust. Add 1 tsp more milk powder or a pinch more butter to keep it tender.

Baking powder and soda

Bakeries often use ammonium bicarbonate (baker's ammonia) for an even crisper crackle. Use ¼ tsp in place of both, and bake in a ventilated kitchen.

Bread flour (dough)

All-purpose flour works but the buns are less tall and stretchy. Cut the dough milk by 10 ml.

Variations

Custard-filled bolo bao

Wrap 20 g of cold, thick custard into each dough ball when shaping and pinch tightly closed.

Matcha topping

Replace 6 g of the topping flour with matcha powder for a green, lightly bitter crust.

Troubleshooting

Topping slid off or spread down the sides

The topping was too soft or too thick, or contained too much leavening. Chill it, roll it no thicker than 4 mm and measure the leaveners with level spoons.

No cracks in the crust

The topping was too wet or rolled too thin. Add a spoonful of flour, keep the discs at 4 mm, and score lightly if needed.

Buns are dense under the crust

They were underproofed. Wait until they are clearly puffy and spring back slowly before adding the topping.

Storage

The crust is crispest within a few hours. Store cooled buns in a bag at room temperature for up to 2 days, then rewarm at 160°C (325°F) for 5 minutes to recrisp the top. Freeze for up to 1 month.

Safety notes

Do not taste raw dough or raw topping; both contain uncooked egg and flour. Contains wheat, egg and milk.