WHAT YOU NEED

For the biscuit
40g icing (confectioners’) sugar
250g unsalted butter, softened
225g plain (all-purpose) flour, plus extra for dusting*
75g custard powder**
1 tsp baking powder
¼ tsp salt flakes

For the marmalade buttercream
100g unsalted butter, softened
85g icing (confectioners’) sugar, plus extra for dusting
Zest and juice of ½ orange
1 heaped tbsp orange marmalade

* You can use cornflour (cornstarch) if you don’t have custard powder; if so, add 1 tsp vanilla extract or vanilla bean paste PLUS an extra 1 tbsp icing sugar to your biscuit mixture.

**Amazingly, gluten-free flour is just as good here!

To make the melting moments
Line two light-coloured (see Tips below) baking trays (ideally biscuit trays) with baking paper.
If your icing sugar is lumpy, pop it into a food processor and blitz, or into a zip-lock bag and mash with a rolling pin.
Using a stand mixer with the paddle attachment, beat the softened butter until uniformly soft, then add the icing sugar, and beat until the mixture is pale and creamy (more is more here).
Sift together the flour, custard powder, and baking powder. Add to the butter mixture, along with the salt, and mix with a wooden spoon until just combined.
Use a teaspoon measure dusted with a smidge of flour to scoop out 2 level tsp of the mixture, rolling into walnut-sized balls between your hands. If your hands are hot, pat a little flour onto them to stop the mixture sticking. Evenly space the balls out on the baking trays. Don’t worry if they’re a bit mangy; you can always smooth them out once chilled.
Pop the trays in the fridge to chill for 15 minutes, or even overnight.
When ready to bake, preheat the oven to 150°C. Use a floured fork to press each dough ball into a 2cm disc.
Bake for 15–18 minutes, until the biscuits are set enough to be dislodged with a gentle prod, are custard-yellow in colour, and the bottom is still blonde. Allow to cool for 10 minutes, then cool completely on a wire rack before filling.
Make your buttercream in the stand mixer by creaming the butter and icing sugar together until super pale. Add the orange zest, juice, and marmalade and beat until incorporated.
To fill the biscuits, either transfer the buttercream to a piping bag and squeeze it over half the biscuits or spread a teaspoon of filling over them. Pop the unfilled biscuits on top of the filled ones like hats, squashing ever so slightly to more evenly distribute the filling.
Give the whole lot one last dusting of icing sugar as a final flourish.
The biscuits will keep in an airtight container in a cool place for up to five days. They can also be frozen (filled or unfilled) for up to three months; thaw for at least 30 minutes before serving.

Tips
There are entire books and blogs dedicated to tweaking the various variables of the biscuit/cookie caper, but some tricks of the trade are so tried and true that you simply must capitulate—after all, it’s science!

• For evenly coloured biscuits, using an aluminium or lighter-coloured biscuit tray will make all the difference—the darker the tray, the more heat it absorbs, which leads to toasty bottoms (not in a good way, sadly). Biscuit trays are also almost entirely flat, which means that the heat can access each side of the biscuit evenly.
• Place any leftover dough on a piece of baking paper, roll up into a log (twisting the edges so it looks like salami) and stash in the freezer. When you have a hankering, simply slice off 1cm pieces and bake as normal.
• The more butter/fat you add to the dough, the ‘shorter’ your biscuit will be, meaning the more easily it crumbles.