1 First start by making your dough: mix together the flour, sugar and salt in a large bowl. Now cut the chilled butter into 1-inch cubs and add to the flour.
2 Wash your hands with super cold water before using your fingertips to rub the butter into the flour until the mixture resembles coarse breadcrumbs (this could take up to 15 minutes so be patient with it).
3 Add 1 tablespoon of cold water at a time to the mixture and use a wooden spoon to fold it together after every addition. Stop adding water when the dough begins to form large clumps (I used 6 tablespoons/90ml in total).
4 Lightly dust a clean work surface with flour, before scrunching the dough up in your hands and transferring from the bowl to the worktop. Using your hands fold the dough in on itself so all the flour is incorporated and the dough has come together (this should happen easily and the dough shouldn’t be sticky). Flatten the dough into a disk; tightly wrap it with cling film and place in the fridge for at least 2 hours or up to 4 days.
5 Once the dough is chilled, it’s time to make your hearts: Preheat the oven to 180°C and line two large baking trays with greaseproof paper.
6 Lightly dust a clean work surface and your rolling pin with flour. Roll the dough from the centre outwards until it’s smooth and even, roughly ¼ inch (6mm). Use your cookie cutter to cut out as many hearts as you can. Recombine the scraps of dough and repeat until you have 20 hearts in total.
7 Next up, spoon ½ teaspoons of cherry jam in the center of 10 of the hearts. Remember to leave a border around the outside of each heart.
8 In a small bowl beat the egg with a splash of water. Using your fingertip, run a bit of egg wash along the border of the jam-filled heart. This creates a seal for heart tops. Now start placing the jam-free hearts on top on of the jam-filled ones and use a fork to pinch the edges together.
9 Before baking, give the top of each pie a light coating of the egg wash, to help them get golden and crispy, and sprinkle with a little white sugar.
10 Bake for 25-30 minutes until they’re golden brown and the bottom of each heart has hardened (check by carefully lifting one up with a knife – no soggy bottom’s here!) Don’t panic if the jam has leaked a little, this is normal and the pies will still be jam-packed inside.
11 Store your mini-heart pies at room temperature for up to two days. Or store in the fridge in an airtight container for up to five days.