In a mixing bowl, using an electric mixer, on low speed, thoroughly combine all of the dry ingredients. Add the butter and the egg. Mix until the dough comes together in a nice ball. Form the dough into 24 balls.
Preheat the oven to 350 degrees F.
Put the balls on cookie sheets that have either been lined with parchment paper or slightly (very slightly) greased with butter. Gently press the balls with your thumb, ever so slightly, squishing the ball. If you are not using parchment paper, lift the balls from the sheet and then put them back, this will avoid sticking later on.
Bake for 8 to10 minutes, checking the cookies periodically. You can rotate the cookie sheets after 4 minutes to ensure that the cookies are baking evenly. Remove the pans from the oven and put the cookies on a cooling rack or a clean surface. Allow them to cool at least 15 minutes.
Filling: Put the butter, shortening, and vanilla into a bowl, and mix with an electric mixer on low speed. Gradually add the powdered sugar and mix until the filling is light and fluffy.
When the cookies are cool, smear a small amount of the filling on 1 side of half of the cookies. Top with the remaining cookies, creating that famous whoopee-pie look. Refrigerate the cookies for about 20 minutes before serving.
To add a touch of elegance to this dessert, try infusing milk with lavender. Add a little milk, 1 tablespoon of honey, and a little crushed lavender to a blender. Blend on high for about 3 minutes. Refrigerate for about 20 minutes, then stir with a spoon and serve!
Dip the cookies in a cool glass of milk, if desired.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.