Preheat the oven to 325˚F. Line two muffin pans with cupcake liners. Set aside.
Cupcakes: In a medium bowl, cream together the butter and the sugar until light and fluffy. Add in the eggs one at a time, and beat until fully combined. Mix in the lemon juice and vanilla bean paste.
In a separate bowl, mix together the flour and baking powder. Slowly mix the dry ingredients into the wet ingredients until fully incorporated.
Fill the prepared cupcake liners with batter, around 3/4 full.
Bake in the preheated oven for 15 minutes, remove and rotate pans, then bake an additional 15 minutes, or until a toothpick inserted comes out clean. Remove cupcakes from the oven, and place on wire racks to cool completely.
Frosting: In a medium bowl, beat the butter on medium speed for around 2-3 minutes, until smooth and creamy. Add the icing sugar, and beat until fully incorporated. Add in the Nutella, milk and vanilla bean paste and mix until fully combined. If the mixture is too thick, add more milk. If it is too thin, add more icing sugar until the frosting reaches your desired consistency. Pipe onto the cooled cupcakes.