Bake cupcakes according to package instructions making sure to only fill the cupcake liners no more than 2/3rds full.
While the cupcakes bake, make the lemon blueberry sauce by whisking together in a saucepan the sugar, cornstarch, lemon juice, salt, and vanilla extract. Add the blueberries and stir.
Cook the blueberry mixture over medium heat, stirring frequently until the sauce is boiling. Mash down most of the blueberries using the back of spoon or potato masher so that the sauce will fill the holes that will be poked in the cupcakes.
Remove the pan from the heat and mix in the lemon zest. Set the pan aside to so the sauce can cool.
Once the cupcakes have been removed from the oven, poke holes in them using the handle of a wooden spoon (I poked about 4 holes per cupcake). Then fill each cupcake with the lemon blueberry sauce and place some of the sauce on top of the cupcake (about 2 tablespoons per cupcake).
Allow the cupcakes to cool completely, then make the whipped topping. Place your cold heavy cream in the bowl of a stand mixer with the whisk attachment.
Begin whipping the heavy cream on medium speed until soft peaks form. While the mixer is running, slowly add in the powdered sugar.
Continue to mix until medium peaks form. However, be careful not to whip the cream too long otherwise you will end up looking curdled and begin to turn into butter.
Top each cupcake with the whipped cream and decorate the top of the cupcakes with blueberries or lemon slices. Enjoy.
Store leftovers in the refrigerator.