Raspberry & vanilla Valentine hearts

Tip the raspberries into a mini blender or food processor and pulse until finely chopped. Set aside.

Put the icing sugar and butter in the bowl of a stand mixer (or a large bowl with an electric hand mixer) and beat until pale. Add the vanilla extract and lemon zest, then mix to combine.

Add the egg yolks, one at a time, mixing well between each addition. Sift the flour, baking powder and a pinch of salt into the bowl. Add the raspberries and mix gently to a smooth dough. Don’t overwork the dough or the biscuits will be tough rather than crisp and light-textured. Gather the dough into a neat disc, wrap and chill for at least 1 hour, or until firm.

Line 2 large baking sheets with baking parchment. Dust the work surface with flour and roll the dough out to 0.2-0.3cm thick. Using a 7cm heart shaped cutter, stamp out shapes from the dough and arrange on the lined baking sheets. Chill for 15 minutes while you preheat the oven to 170ºC, gas mark 3.

Bake the biscuits on the middle shelf for 12-14 minutes, depending on size, until crisp and starting to turn golden at the edges. Leave to cool on the baking sheets for 5 minutes, then transfer to a wire cooling rack until cold.

To decorate, put the egg whites and a pinch of salt into a large bowl, and use electric beaters to whisk until frothy. Gradually add 200g of the icing sugar a little at a time, then beat until smooth and thick enough to coat the back of a spoon. You may need to add a little more icing sugar, for the correct consistency. Mix in the colouring gel for the desired colour – for a really vibrant colour you might need 1-2 tubes.

Tip the remaining 100g icing sugar into a bowl, stir in 1-11/2 tbsp water to make this the same consistency as the coloured icing and beat well. Spoon the white icing into a disposable piping bag and snip the end into a fine point.

Taking one biscuit at a time, dip the top into the coloured icing to neatly coat, allowing any excess icing to drip back into the bowl, then lay back on the cooling rack. Using the white icing, pipe neat thin lines – each about 1cm apart – across the heart. Using a wooden skewer or cocktail stick, drag the point through the white icing to feather. Repeat with the remaining biscuits, allow to set firm, then serve.