In the bowl of a stand mixer combine the mascarpone cheese, powdered sugar, and lemon zest. Blend until smooth. Turn the mixer on low and slowly add the whipping cream until it's incorporated and starting to thicken. Increase the speed to medium, then high, and beat until medium peaks form. It won't take long.
Transfer ⅓ of the cream to a container with a tight fitting lid and refrigerate until needed. This will be used to "ice" the cake.
Gently fold in ½ cup of lemon curd into the remaining mascarpone mixture. Now you're ready to assemble the icebox cake.
Place a layer of pound cake in the bottom of the prepared pan, cutting to fit as needed. Spread ¼ of the lemon cream over the cake and use the back of a spoon to smooth the surface (place the remaining lemon cream in the refrigerator until needed again).
Place the pan in the freezer for 5-10 minutes, then spoon ½ cup of the blueberry sauce in mounds over the lemon cream. Spread gently with a clean spoon to cover the cream. Place the pan back in the freezer for about 10 minutes.
Drizzle ¼ cup of the lemon curd over the blueberry sauce. Spoon ⅓ of the remaining lemon cream over the curd and smooth evenly with the back of a spoon. Top with another layer of pound cake.
Repeat the process with ½ of the remaining lemon cream, ½ cup blueberry sauce, and the remaining lemon curd, freezing between layers as needed.
Finish with a layer of lemon cream and a final layer of pound cake. The cake may extend over the top of the pan depending on how thick you cut the pound cake. This is where you need that extra long pieces of plastic wrap to come up and over the cake to hold it all in.
Wrap the entire cake in plastic wrap and freeze for at least 8 hours or overnight.
When ready to serve, remove the plastic wrap and invert the cake onto a serving platter. Peel off the plastic wrap and trim the sides of the cake with a knife, if desired, to make a straight edge.
Spread the top and sides of the cake with the remaining mascarpone cream. If needed, whisk the cream until soft peaks form again.
Place the iced cake in the freezer at least 15 minutes or until ready to serve.
To serve, mix the ⅓ cup fresh blueberries into the remaining blueberry sauce and spoon over the cake.