Preheat the oven to 180C/350F and line 2 baking trays with grease proof paper/a silicone mat.
Leave your unwrapped chocolate kisses in a bowl to the side and cover with a kitchen paper.
Place the butter and sugar into a large bowl, or the bowl of your stand mixer and beat on medium speed until light and fluffy. Around 2 minutes.
Add in the egg yolk and vanilla extract, scraping down the sides as necessary, and beat until well incorporated and smooth.
Add in the flour, cornflour and salt and mix on low until the mixture begins to come together. Once it comes together, turn the speed up to medium until you have a smooth dough with no lumps of flour.
Take 1tbsp of dough and roll into a ball, place on your prepared baking tray and then flatten slightly with your palm. Either use a small rolling pin or your thumb to make an indentation in the middle of the cookie. Repeat until you have 24 cookies placed 2 inches apart on your baking trays.
Place in the oven for 10-14 minutes (mine took 11 minutes) until golden around the edges and risen.
Remove from the oven and immediately place a chocolate kiss into the centre of each cookie where you made the indentation.
Leave to cool for 5 minutes before digging in.
You can also enjoy these at room temperature, but when warm, the chocolate is gooey and melted. You can store the cookies in an airtight container, at room temperature for 5 days. Warm in the microwave for 30 seconds if you want them warm.