• I like to measure out all my ingredients ahead of time (even a day ahead) so prep time is a breeze. You can do this or measure as you go -- make sure you set out your butter for the biscuits and filling (112 g each) several hours prior or the night before in an air-tight container so that it comes to room temp

Make the Biscuits | Cookies

• Preheat oven to 325 F. Line baking sheets with parchment paper and set aside
• In the bowl of a stand mixer fitted with paddle attachment, place the flour, xantham gum, cornstarch, powdered sugar and salt and combine. Add the lemon zest, and mix to combine.
• Add the butter in 2-3 additions, mixing between each; scrape down the bowl, then add your egg while mixing to combine on low. The dough will come together in a smooth and relatively thick mixture.
• Place the dough between two sheets of parchment and roll out to about 1/8th (or slightly over) thick. Place the dough and parchment on the back of a backing tray or a flat surface and freeze for 7 minutes to firm
• Remove the dough and the top parchment paper and use a circle or oval cooking cutter to cut out shapes (we used a mixture of a 1.5-inch circle cutter and a 2-inch circle cutter). Remove your circles to the parchment lined baking sheet using a spatula. You will likely need to repeat this process a few times as you will have dough scraps left over. You can determine if you need to re-freeze between each rolling (you can always pop the ball of dough in the freezer, then re-roll)
• Place the first baking sheet in the center of the oven until just cooked through and firm and just slightly starting to turn golden on the outside, 12-15 minutes depending on size, color of baking sheet and thickness. Our 1.5-inch circles took 12 minutes; our 2-inch took 15 min and we prefer a light colored cookie but one that still has a snap to it
• Remove tray from oven and allow cookies to cool on the tray for 5 minutes before removing them to a wire rack to cool fully

Make the Vanilla Cream

• Depending on the time you have, you can wait until all cookies are baked and cool to make this or make it while cookies are in the oven, and pop in the fridge until ready to use. Keep in mind if you place in the fridge for any length of time it will take an hour or so to come to a usable temperature for piping
• In the bowl of a stand mixer fitted with paddle attachment, cream your butter on medium until light and fluffy. Add the salt and confectioners sugar slowly, and mix on low speed until the sugar is absorbed. Turn the mixer to medium and mix until the filling comes together fully and is super light and fluffy -- 3-4 minutes. It will be quite thick
• Add the vanilla and mix in. Add your 2 tsp milk and mix on medium until the filling becomes smoother and creamy -- it should still be quite thick
• If you are ready to use immediately you can fill a pastry bag fitted with an open star tip or pop in the fridge for 5-10 minutes just to set up a bit more -- the heat from your hands will make the mixture softer
• Turn half the cookies over and place tops beside them. Pipe a generous dollop of filling onto each biscuit bottom. Gently press the top on to move the filling to the edge of the cookie (press in center to avoid breaking the cookies). Allow to sit at room temp or in the fridge until filling is set

Make the White Chocolate Ganache

• You can skip this step if you're pressed for time or would prefer a less sweet sandwich biscuit. Also, we are making a generous amount of ganache so you will have some leftover that you can place in a container and refrigerate
• Place your sandwich biscuits on a wire rack atop a baking sheet lined with aluminum foil (for easy clean-up)
• Place your white chocolate in a microwave safe bowl and microwave for 45 seconds to 1 minute or until slightly softened
• Bring your cream to a simmer on the stovetop (this will happen quickly for this small amount of cream
• Pour the cream over the chips, covering them, and let sit for 5-10 minutes. Stir or whisk to combine until completely smooth
• Place ganache into a piping bag. When ready to go, snip of the end and work quickly several inches above cookies to spread long lines of ganache across the top of the biscuits. The ganache will need to set at room temperature or -- better yet, in the refrigerator
• Enjoy immediately or store in an air-tight container in the fridge