Lemon Sugar Cookies

2¾ cups flour
1 tsp. cream of tartar
1 tsp. baking soda
½ tsp. salt
1 stick butter
½ cup vegetable shortening
1 ½ cups sugar
2 eggs
1 tsp. grated lemon zest
Sanding Sugar (or regular sugar) for decorating


Directions
• Preheat the oven to 400.
• In a large bowl combine flour, cream of tartar, baking soda and salt.
• In a mixer with paddle attachment beat butter, shortening, and sugar on high speed until light and fluffy, about 2 minutes. Scrape down the sides and add the eggs and lemon zest, and mix until fully incorporated. Then, add the flour mixture and mix at medium-low speed until just combined.
• Using a rounded ½ tablespoon, roll the dough into balls and then roll them in the sanding sugar.
• Place the dough about 2-3 inches apart on a cookie sheet.
• Bake for 8-10 minutes until the edges start to turn gold. Let cool completely on rack.


Filling Ingredients
½ cup (1 stick) softened butter
½ cup solid vegetable shortening
3½ cups confectioners' sugar
2 tsp. grated lemon zest (about 1Ž2 lemons)
½ tsp. citric acid (or sour salt, it is usually with the spices in the supermarket) It really gives the filling the tartness to balance the sweet buttery cookies.
• Beat all filling ingredients together until mixture is smooth and thick. • Spread one cookie with filling to the edge and top with another of the same size.