Ingredients

Equipment Needed

• •Mixing bowl
• •Wooden spoon or electric whisk
• •Rolling pin
• •Sharp knife or rectangular cutter
• •Two baking trays
• •Baking parchment
• •Wire cooling rack
• •Piping bag with a small round nozzle, optional

Instructions

1. 1

   Cream butter and sugar

   Put the softened butter and caster sugar in a bowl and beat them together until pale and light. A wooden spoon is fine; an electric whisk is faster. You're after something that looks like thick cream and has lost its graininess. Add the vanilla and beat it through.

   The butter has to be properly soft. Not melting, not greasy, but giving easily under your finger. Cold butter will fight you the whole way and you'll lose.
2. 2

   Bring the dough together

   Sift the flour, custard powder, baking powder and salt straight into the bowl. The custard powder is the whole point here, that pale yellow colour and the faint, nostalgic vanilla-and-something-else smell that tells you exactly what biscuit you're making. Mix gently with a wooden spoon, then bring it together with your hands. If it feels dry and won't quite cohere, add a tablespoon of milk. You want a soft, pliable dough, not a sticky one.

   Don't overwork it. The moment it comes together into a single piece, stop. A worked dough makes a tough biscuit.
3. 3

   Rest the dough

   Flatten the dough into a disc, wrap it in cling film or baking parchment, and put it in the fridge for twenty minutes. This isn't optional. Cold dough rolls cleanly and holds its shape in the oven. Warm dough spreads and loses its edges, and the whole point of a custard cream is the edges.

4. 4

   Roll and cut

   Heat the oven to 170C/150C fan. Line two baking trays with parchment. Roll the dough out on a lightly floured surface to about 4mm thick. Not paper-thin, but not chunky either. Cut into rectangles, around 4cm by 5cm, with a sharp knife and a ruler if you care about neatness, or freehand if you don't. You should get around thirty-two pieces, which makes sixteen sandwiched biscuits. Lay them on the trays with a little space between, then prick each one a few times with a fork. The fork holes are tradition. They also stop the biscuits from doming.

   If you have a custard cream stamp or an embossing tool, by all means use it. Most of us don't. A fork makes a perfectly handsome biscuit and looks like it was made by a person, which it was.
5. 5

   Bake until pale gold

   Bake for twelve to fifteen minutes, until the biscuits are firm to the touch and just starting to colour at the edges. Don't wait for deep gold. You want them pale and sandy, the colour of the inside of a digestive, not the outside. They'll firm up as they cool. Lift them carefully onto a wire rack and leave them completely cold before you fill them. Warm biscuits and buttercream is a disaster you only make once.

6. 6

   Make the custard buttercream

   Beat the very soft butter on its own for a minute until pale and fluffy. Add the sifted icing sugar and the custard powder a bit at a time, beating between additions so it doesn't fly out of the bowl. Add the vanilla. Beat for a couple of minutes until the buttercream is properly light, almost mousse-like, and the colour has gone from white to pale primrose yellow. If it feels stiff, add a teaspoon of milk. Taste it. It should taste of vanilla and butter and something that reminds you of being seven years old.

   Sift the icing sugar properly. Lumps in buttercream are sad and entirely avoidable.
7. 7

   Sandwich and finish

   Match the biscuits up in pairs by size. Spoon or pipe a generous teaspoon of buttercream onto the flat side of one biscuit, then press its partner gently on top until the filling just reaches the edges. Not squeezing out, not stingy. Somewhere in between. Repeat with the rest. Leave them for half an hour for the filling to settle, if you can manage the wait.

Chef Tips

• •Custard powder is the soul of this biscuit. Bird's is the standard and there's no improving on it. Don't try to substitute cornflour or vanilla pudding mix. They taste of nothing in particular and you'll wonder why your biscuits have lost the plot.
• •Bake them paler than you think. A custard cream wants to be the colour of straw, not toast. Deep golden biscuits are delicious but they aren't custard creams. The colour matters because the memory matters.
• •Stored in an airtight tin, they keep beautifully for four or five days, and the texture actually improves overnight as the filling softens the biscuit very slightly at the join. Make them on a Sunday and you'll be glad of them all week.
• •If you have a piping bag, use it for the filling. A round nozzle gives you a tidier line and slightly less mess. If you don't, a teaspoon and a steady hand do the job perfectly well.

Advance Preparation

• •The biscuit dough can be made a day ahead and kept wrapped in the fridge. Let it sit out for ten minutes before rolling so it doesn't crack.
• •The unfilled biscuits keep in an airtight tin for up to a week. Fill them on the day you want to eat them, or the day before at the earliest.
• •Sandwiched biscuits keep in a tin for four to five days and are arguably better on the second day, once the filling has settled.

Frequently Asked Questions

Nutrition Information

1 serving (about 47g)