Preheat a non-convection oven to 350F.
To make the shortbread
In a stand mixer fitted with the paddle attachment, place butter in bowl and mix on low speed until soft. Slowly add the powdered sugar, lemon zest, vanilla extract, and salt and beat until well incorporated. Then gradually add the flour and continue to mix until the dough has come together. Press the dough into a disk and wrap in plastic film and refrigerate for 5 minutes. Place dough on a lightly floured work surface. Roll the dough out to 1/8 thickness. Using a 3” pastry cutter, cut out cookies and place on a half baking sheet that has been lined with parchment paper. Place cookies in oven for 10 minutes or until lightly golden. Cool cookies completely before filling.
To make the strawberry jam
In a small bowl, stir together the 2 tablespoons sugar and pectin. Set aside. In a medium pot, combine the strawberries and the sugar and bring to a simmer over medium heat, stirring occasionally. Sprinkle the sugar-pectin mixture over the strawberries and stir until it fully incorporates. Continue stirring for 4 to 6 minutes until the mixture has thickened. Remove from heat and let cool in an ice-water bath. Reserve until needed.
To make the vanilla buttercream
In a stand mixer with a paddle attachment, add cream butter and shortening until light and fluffy. On low speed, stir in salt and vanilla extract and mix. Next, add the powdered sugar and mix until fully incorporated. Place the buttercream in a pastry bag, fitted with ½ inch pastry round tip.
To assemble the cookie sandwich
Pipe buttercream in a circular motion on one side of the cookie. Place 1 tablespoon of strawberry jam in the middle of the cookie. Place the top of the cookie to close off the sandwich.
Pour a glass of Kendall-Jackson Vintner’s Reserve Riesling. Enjoy!