Preheat the oven to 180C/350F/Gas 4, and line a baking tray with parchment paper, or a silicone mat. Set aside.

In a large mixing bowl, beat together the butter and sugars until smooth and combined. Add the egg yolk and vanilla, and mix until combined.

Add enough red food colouring to reach desired shade.

Add the flour and salt, and mix to form a smooth, soft dough. Use your hands to help bring it all together.

Roll the dough into 0.7oz balls. Roll each one in granulated sugar, and place onto the prepared baking tray.

Use your thumb, or the back of a measuring spoon (I used a 1/2 teaspoon measuring spoon), to make an indent in the middle of each ball.

Bake for 10 - 12 minutes, or until firm to the touch. If the indents have risen, gently press them back down with the measuring spoon.

Allow to cool for 5 minutes before transferring them to a wire rack to cool completely.

In a medium mixing bowl, beat together the cream cheese, butter, and vanilla until smooth and combined.

Add the icing sugar and mix until smooth and combined.

Add more sugar if the mixture is too thin, or add milk (1 tablespoon at a time) if the mixture is too thick.

Fill the indents in the cookies with the filling, and allow to set before serving.