Preheat the oven to 350f (180c). Line a muffin/cupcake tin with paper liners. Sift the flour, cocoa powder, espresso powder, salt and baking sugar into a large bowl. Briefly whisk to combine.
In another bowl, combine the egg, sour cream, vanilla, sugar and oil. Whisk until smooth.
Divide the mixture (I like an ice cream scoop) between the paper liners, ensuring they are just a little more than half full. Bake for 15 minutes in the middle of the oven, until a skewer comes out clean.
Leave the cakes to cool until they are at room temperature. Meanwhile, make the frosting!
For the frosting, whip the heavy cream, rose water, food colouring and powdered sugar until it is at the soft-peak stage. Add the mascarpone and whip again to combine. The frosting should be thick and creamy.
Pipe the frosting onto the cakes as desired, and top with mini eggs.