- For the cookies, using electric beaters or a stand mixer fitted with the paddle attachment, beat the butter until smooth. Add the icing sugar. Starting on low speed, work in the sugar, and then increase the speed to medium-high and beat until fluffy, about 2 minutes.
- Beat in the egg yolks and vanilla and rum extracts. Add the flour, salt and nutmeg and beat until the dough comes together. Shape the dough into 2 discs, wrap in plastic and chill for at least 2 hours.
- Preheat the oven to 325°F (160°C) and line 2 baking trays with parchment paper.
- On a lightly floured surface, knead the first disc of dough a little to soften it and then roll it out to just under ¼ inch (6 mm) thick. Use a 2-inch (5 cm) cookie cutter to cut out cookies. Place on the baking trays, 1 inch (25 mm) apart. Repeat with the second disc of dough, re-rolling any scraps as needed.
- Bake the cookies for 12 to 14 minutes, or until slightly golden at the edges. Transfer to a wire rack to cool.
- For the buttercream, beat the butter with 1 cup (130 g) of the icing sugar on medium speed using electric beaters or a stand mixer fitted with the paddle attachment. Once the butter and icing sugar are well blended, add the custard powder, cream, vanilla, and rum extracts and nutmeg. Beat again, starting on low and increasing the speed until all the ingredients are combined (the buttercream may not be smooth at this point).
- Beat in the remaining 1 ¼ cups (160 g) of icing sugar on low and then increase the speed to medium-high and beat for 2 minutes, until fluffy.
- Spoon the buttercream into a piping bag fitted with a small star tip. Pipe a single layer of buttercream onto the bottom of a cookie and gently press a second cookie on top. Repeat with the remaining cookies.
- Use leftover buttercream to pipe a little accent on top of each cookie, then place a silver dragée on top. Let the cookies air-dry for 1 to 2 hours.
You can store these baked cookies in a single layer in an airtight container for1 week at room temperature. Or make the dough and the buttercream ahead. Freeze the dough, shaped into a disc and well wrapped, and the buttercream, spooned into a resealable bag or container, for up to 3 months. To bake, thaw the dough overnight in the fridge before rolling, cutting, filling, and putting the cookies in the oven. Thaw the buttercream at room temperature until soft, then beat it to fluff it up before piping.
Recipe from Set for the Holidays with Anna Olson, Appetite by Random House, 2018