Cream the Butter and Sugar: In a large bowl or the bowl of a stand mixer fitted with the paddle attachment, beat the softened 170g of butter and 150g of caster sugar on medium-high speed for about 3-4 minutes, or until the mixture is light, pale, and fluffy. For a full explanation of this essential step, BBC Good Food has a great guide.

Add Wet Ingredients: Scrape down the sides of the bowl. Add the egg, vanilla extract, and espresso powder. Beat again on medium speed until everything is well combined, about 1 minute.

Combine Dry Ingredients: In a separate bowl, whisk together the 180g plain flour, 60g cocoa powder, bicarbonate of soda, and salt.

Form the Dough: Add the dry ingredients to the wet ingredients in two batches, mixing on low speed until just combined. Be careful not to overmix. The dough will be very soft and sticky at this point.

Chill the Dough: Scrape the dough onto a piece of cling film, form it into a disc, and wrap it tightly. Chill in the refrigerator for at least 1 hour, or until firm. This step is non-negotiable!

Prepare and Bake: Preheat your oven to 180°C (160°C fan) and line two baking trays with parchment paper. Roll the chilled dough into small balls, about 2cm (or 1 tablespoon) each. Place them a few inches apart on the prepared trays. Gently flatten each ball with the palm of your hand. Bake for 10-12 minutes. The edges should be set, but the centres will look slightly underdone. I find that tapping the baking tray on the worktop once or twice as soon as it comes out of the oven helps create a flatter surface for sandwiching.

Cool Completely: Let the cookies cool on the baking trays for 5 minutes before transferring them to a wire rack to cool completely. They must be fully cool before you attempt to fill them.

Make the Raspberry Filling: While the cookies cool, make the filling. In a medium bowl, beat the softened 115g of butter with an electric mixer until creamy. Gradually add the 240g of sifted icing sugar, beating on low speed at first, then increasing to high until smooth. Beat in the raspberry jam and a few drops of food colouring, if using. If the frosting is too stiff, add a tablespoon of milk or cream to reach a smooth, pipeable consistency.

Assemble the Sandwich Cookies: Pair up the cooled cookies by size. Pipe or spread about a teaspoon of the raspberry filling onto the flat side of one cookie and gently press another cookie on top to create your sandwich. Repeat with the remaining cookies.