Start the cupcakes by lining a baking tray with paper liners. In a large bowl, whisk together the egg and sugar until fluffy, then mix in the water, oil, red coloring and cocoa. Finally mix in the flour and bicarbonate of soda. Spoon into the cupcake liners 2/3 full. Bake in the oven at 180`c for 15-20 minutes. Meanwhile, make the buttercream by beating the unsalted butter in a bowl for 10 minutes until light and fluffy. Add in the condensed milk and continue to beat for 3-4 minutes. When the cupcakes are ready and cooled, cut off the tops and fill with the chocolate and hazelnut spread and put the tops back on. Color the buttercream red and pink and pipe onto the cupcakes. Decorate with Valentine’s decorations, hearts and sprinkles and place them into a presentation box.