Put the butter, sugars and vanilla in a mixing bowl and beat together until pale and creamy. Stir in the egg and flour and mix until smooth.
Stir in the fudge and cherries then spoon 18 mounds on to 2 baking sheets lined with nonstick baking paper, leaving space between for them to spread during cooking.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 10–12 minutes until golden brown. Leave to harden for 1–2 minutes then loosen and transfer to a wire rack to cool completely. These are best eaten on the day they are made.