Lemon Mascarpone Tart

Pistachio Graham Crust: Add the graham crackers, pistachios, and sugar to a food processor and pulse to fine crumbs. Add in the melted butter and pulse until the mixture is fully combined.
Press the crust mixture into the bottom and up the sides of a 9” round tart pan. Bake at 350°F for 10-12 minutes. Set aside to cool.
Lemon Mascarpone Mousse: In the bowl of a stand mixer fitted with a whisk attachment, add the mascarpone cheese and cream cheese and mix just until combined. With the mixer on low speed, slowly stream in the heavy cream. Once all the cream is in the bowl, add the powdered sugar, lemon flavoring, and zest. Continue whipping, increasing the speed to medium, until the cream has thickened and is fully incorporated. Turn the mixer to high speed and whip until the mixture is thick and looks like stiff peaks, about 20-30 seconds.
Assembly: Fill a piping bag fitted with a small to medium French-style piping tip, with about 1 cup of the lemon mascarpone mousse. Fill the cooled tart shell with the remaining mousse, spread it out to the edges, and smooth the top with an offset spatula.
Pipe the reserved filling on the top of the tart with star and swirl designs. Finish with slices of fresh lemon and a sprinkle of pistachios, if desired. Chill the tart for about 1 hour. To remove the tart from the pan, push the base of the pan to remove the sides then slide off the removable base. Slice up and enjoy!