For the cupcakes: Position an oven rack in the center of the oven and preheat the oven to 350 degrees F. Line a 12-cup muffin tin with cupcake liners and spray the liners lightly with cooking spray.
Sift the flour, confectioners' sugar and salt through a fine sieve into a medium bowl; stir in the sprinkles and set aside.
Combine the egg whites in a bowl and beat with an electric mixer on medium speed until frothy, about 2 minutes. Add the cream of tartar and beat until soft peaks form, about 2 minutes. Gradually add the granulated sugar, about 1 tablespoon at a time. Increase the speed to medium-high, and continue beating until the peaks are stiff and very shiny, about 5 minutes. Beat in the vanilla and lemon zest. Remove the bowl from the mixer.
Sprinkle 1/4 of the flour mixture over the egg whites and gently fold in with a rubber spatula. Fold in the remaining flour mixture in 3 additions.
Divide the batter evenly among the lined muffin cups, mounding it so it's taller than the liners. Bake until the cupcakes spring back when pressed gently with your fingertip and a toothpick inserted in the centers comes out clean, 14 to 16 minutes. Let cool in the pan for a few minutes, then transfer to a rack to cool completely. (The cupcakes can be made a day ahead and stored at room temperature in an airtight container.)
For the frosting: Put the cream cheese and confectioners' sugar in a medium bowl and beat with an electric mixer on medium-high speed until smooth. Add the heavy cream and vanilla and continue to beat until the mixture forms stiff peaks. (The frosting can be made and refrigerate up to 1 hour before serving.)
When ready to serve, top each cupcake with a generous dollop of frosting. Use the back of a spoon to swirl the frosting a little. Decorate each cupcake with some sprinkles.