Preheat oven to 450 degrees

Place the water, butter, ¼ cup sugar, zest of half the lemon, and salt in a heavy-bottomed pot and bring to a boil over medium high heat. Add the flour and stir until the flour is completely incorporated. Continue to cook and stir for 3 to 4 minutes to remove as much steam as possible.

Move the mixture to the bowl of a stand mixer fitted with the paddle attachment. Beat the mixture on medium for about 1-2 minutes to allow it to cool. Add one egg yolk. Mix it mix in completely incorporated and then scrape down the sides of the bowl, if needed. Add the remaining egg yolks, one at a time, and mixing in completely between each addition. Add the egg whites and mix until the paste will hold a slight peak when pinched with your fingers. Transfer the batter to a ziplock bag, pushing the batter to one of tips. Cut the tip to use for piping.

Pipe the batter into a doughnut pan that has been sprayed with non-stick spray. Make sure that the batter is as even as possible using an off-set spatula. Bake for 5 minutes, then reduce heat to 350 and bake for another 15 minutes. Turn off the heat, open the oven door slightly and let the doughnuts sit in the oven for another 5 to 10 minutes.

While the doughnuts are baking, make the lemon mascarpone icing. Mix together juice of 1 lemon, remaining half of the lemon zest, the softened mascarpone cheese, remaining ¼ cup of sugar, and vanilla until evenly distributed. If icing is thick and is unable to be drizzled - add in 1-2 tbsp. of milk if needed to thin.

Remove doughnuts from oven and place on a rack to cool, drizzle with lemon mascarpone icing, and top with berries.