Red Velvet Shortbread Cup Cake

Name: Red Velvet Shortbread Cup Cake
Ingredients: 250 grams of butter, softened; 140 grams of caster sugar; 1 egg yolk; 2 teaspoons vanilla extract; 300 grams of plain flour; 60 grams of unsalted butter; 150 grams of caster sugar; 1 egg; 10 grams of cocoa powder; 20 milliliters red floor colouring; 0.5 teaspoons vanilla extract; 120 milliliters buttermilk; 150 grams of plain flour; 0.5 teaspoons salt; 0.5 teaspoons bicarbonate of soda; 1.5 teaspoons white wine vinegar; 140 grams of softened butter; 280 grams of icing sugar; 1 tablespoon milk