Shortbread cookies made with a simple buttercream and plum butter filling. A delicious pastry cookie recipe that is great for holidays and parties.
Preheat oven to 350°F with the rack in the middle.
Combine 1 tsp baking soda with 1 tbsp vinegar in a cup and stir until the foam subsides.
Cream together 1/2 cup butter with 1 cup Crisco shortening and 1 cup sugar for about 1 minute with a mixer. Add 1/2 cup of sour cream, 2 egg yolks, 1 egg and the baking soda+vinegar mixture and mix until combined. Now add 3 cups sifted flour and mix until it comes together. Once the flour is mixed in, add one more cup and mix it in by hand. Split the dough into 4 equal pieces and refrigerate for at least 30 minutes before rolling.
Whip 2 sticks butter and 1 tablespoon of vanilla extract for about 5 minutes or until very white/pale in color and increased in volume.
Now cut 1 cup cream cheese into smaller pieces and add them into the whipped butter a couple of cubes at a time, minimally whipping after each addition.
Separately whip 1/2 cup heavy cream, then carefully fold it into whipped butter and cream cheese mixture. Do not overfold, as the mixture separates easily. If the mixture does start to separate, take a couple of spoons of buttercream and microwave it in 5 seconds increments, about 2 or 3 times, then fold it back into the rest of the buttercream. Do so, until the cream comes together. With heating the buttercream, you're just trying to bring it to room temperature, and not make it melt.
Now stir 2-3 tbsp lemon juice and 1 cup powdered sugar together until smooth. Take away couple tablespoons of the glaze and add 2 teaspoons of cocoa powder to it, then stir again until smooth; cover with plastic wrap.
Cookies can be frozen in an airtight container for up to 2 months. To thaw, transfer to fridge and leave there until no longer frozen.