Put butter in the pot and melt it on low heat, add sugar, then sour cream and stir. When the mixture is no longer hot, stir in the egg and vanilla aroma.
Put the flour, baking powder in a bowl and mix, then add the grated lemon zest and pour in the butter mixture and mix everything to combine nicely. The dough comes soft but not runny.
Evenly fill the baking tray for mini muffins, in which you previously arranged the mini baking papers. (A little less than half a tablespoon for each muffin). Then bake in the oven at 180 degrees Celsius for about 13 minutes, making sure that they are nicely colored and do not burn.
Once they are baked, take them out of the baking tray, arrange them on a tray and let them cool down.
For the frosting, you need to have blueberries thawed completely (we can thaw them right under the hot water) and blend them into a puree first. Put mascarpone cheese and sugar in a bowl and mix carefully. Whip the cream and add it to the bowl, and finally add the blueberries.Add frosting on top of the muffins with a piping bag, place a blueberry on top of each cupcake and serve.