These delicate cookies will bring the feeling of spring into your kitchen. Light and crunchy citrus shortbread cookies come together quickly and can be rolled and baked right away. The orange filling is creamy and packed with citrus flavor, making it a perfect match for these adorable sandwich cookies.
Place a rack in the center of the oven and preheat the oven to 350 degrees F. Line 2 sheet pans with parchment paper.
For the citrus cookies: Combine the sugar and lemon and orange zests in a stand mixer fitted with the paddle attachment. Mix on low speed until the zests are rubbed into the sugar and the mixture is fragrant, light yellow and looks like wet sand. Add the butter, oil, baking powder, salt and vanilla and mix on low to combine. Raise the speed to medium and cream until lightened and smooth, 1 to 2 minutes.
Scrape down the sides of the bowl and mix on medium speed for a few seconds. Add the flour all at once and blend on low speed until no streaks of flour remains. The mixture will look dry but will come together. Use your spatula to give the dough a few turns in the bowl to incorporate any remaining flour.
Take about half of the dough and place it between 2 sheets of parchment paper lightly dusted with flour. Roll the dough out until it is just under 1/4-inch thick. Use a 1 1/2-inch round cutter to cut out as many circles as possible, placing 6 rows of 4 cookies per row on a prepared sheet pan (24 per sheet). Bake the first sheet on the middle rack of the oven until evenly golden on the edges and top, 12 to 14 minutes.
While the first tray bakes, reroll any scraps and roll out the second half of the dough to fill the second prepared pan with 24 cookies. Bake the second sheet of cookies after you take the first sheet out. Allow the cookies to cool on the trays 1 hour before filling; they will crisp as they cool.
For the orange cream filling: Combine the white chocolate chips and 1 tablespoon of the butter in a small microwave-safe bowl. Microwave in 15-second intervals, stirring well after each interval, until melted, about 45 seconds. (It’s okay if the mixture separates; it will come together after it’s melted and stirred.)
Combine the remaining 3 tablespoons butter and the orange zest in a separate medium bowl and use a rubber spatula to mix and spread the butter until it is smooth and creamy. Add the confectioners' sugar and mix until smooth. Add the melted white chocolate and mix until smooth.
Place the filling in a disposable pastry bag or sandwich bag and snip off a 1/4-inch opening. Pipe about 1 teaspoon of the filling onto the bottoms of 24 cookies. Top with the remaining cookies to make sandwiches. Serve immediately or allow to rest for a few hours so that the filling can set up. Store at room temperature in an airtight container for up to a week.