Sieve your flour into a large bowl and add the cold, cubed butter and lard to the bowl. Rub the fats with the flour between your fingers until the mixture resembles breadcrumbs. ⠀
Add the sugar and mix to combine.
Beat the vanilla and egg yolks in a small cup, and add to the flour mixture. ⠀
Start gently bringing the dough together until it’s even in colour. Don’t overwork it as that’ll make for a tough biscuit.
Place in the fridge for 30mins to rest. ⠀
Preheat the oven to 180C / 160C fan / 350F.
Remove the dough from the fridge and flour a work surface, rolling the dough to a thickness of half a centimetre. It may want to break apart but persevere. Keep moving it around carefully and ensuring your rolling pin and surface are always floured so it doesn’t stick. ⠀
Using a cookie cutter, cut rounds out, re-rolling any scraps until you’ve used up all the dough. Stamp hearts out of the centre of half the rounds and place them all on a baking tray lined with parchment paper.
Bake for 10mins then transfer to a wire rack and leave to cool completely on the tray. ⠀
Dust the cookies with heart cut-outs with sieved icing sugar, spread raspberry jam on the other half and then sandwich the top and bottoms together. ⠀