Soboro-ppang (Peanut Streusel Bun)

Variations

• With red bean: sweet bean paste inside, soboro outside. The commonest combination on a Korean bakery shelf, and the nuttiness and the sweetness hold each other in check.
• Fried soboro: the Daejeon version, filled with bean paste and deep-fried instead of baked. The topping crisps a second time in the oil and goes much darker.
• Custard soboro: filled with custard, piped in after baking and cooling.
• Without peanut butter: butter, sugar and flour alone still make a soboro. But the smell people recognise is the peanut, and without it this is closer to a German streusel.
• Japan's melonpan: the same idea, but the topping is a single sheet of cookie dough scored into a grid with a knife. Even the way it is applied differs from pressing loose crumbs on.
• Mexico's concha: the third form of the same structure — a sweet paste rolled thin over the bun and cut into a shell pattern. Putting a second dough on top of a sweet bun was arrived at separately in several places.
• The rest of the bakery: brioche, babka, kanelbulle, pain au chocolat, croissants, doughnuts.
• Korea's other flour snack: hotteok. In the bean-paste-inside shape it also overlaps with char siu bao.

Tips

• Do not knead the soboro. The name of the bun rides on this. Rub it with your fingertips only and leave pea-sized lumps; worked into a smooth dough it stretches in the oven and nothing cracks. If it starts coming together, put it back in the fridge to firm the butter.
• The butter in the topping stays cold. Same reason as in pastry: melted butter wets the flour into a dough, cold butter stays in pieces and keeps it crumbly (dairy and heat).
• Wet the top only. Crumbs down the sides seal the bun all round and it has nowhere to push. The cracking happens because it can only rise upward.
• Do not fully prove the second rise. This is the opposite of most bread. Fully proved, the dough collapses under the weight of the topping and has no lift left for the oven. Stopping around 1.7 times is what leaves oven spring to tear the topping open (fermentation basics).
• Bake hot and short. The topping is sugar and butter; a long bake at a low temperature melts it flat and then burns it. 190C for 13 minutes, and judge the colour by the exposed sides of the bun rather than by the topping (what your oven is doing, browning).
• Knead the bun dough properly. It has to carry the topping's weight and then push it apart, and under-developed dough cannot. Stretch a piece until it goes translucent (dough and gluten, choosing flour).
• Keep salt and yeast apart. In direct dry contact the salt kills the yeast. Put them on opposite sides of the bowl and mix the flour through before the liquid goes in.
• Milk no hotter than 35C. Hot milk damages the yeast, cold milk drags the rise out. Lukewarm on the back of your hand is right.
• Do not skip the 15-minute bench rest. Dough tightened by dividing will tear at the surface if you re-round it immediately, and the topping sinks into the tear.
• Eat them cool. Straight from the oven the topping is soft and comes away on your fingers. Twenty minutes of cooling sets the sugar and crisps it, and that crispness against the soft crumb is the point of the bun (what sugar does, serving temperature).
• Freeze the leftovers. By the next day the topping has drawn moisture out of the bun and gone soft. Wrapped individually as soon as they cool and reheated in a toaster oven, the crispness comes back (freezing and thawing, reviving leftovers).
• Keep spare soboro. Freeze what is left over for next time, or scatter it straight onto muffins or a fruit crumble.