6 tbsp. unsalted butter, softened
1/4 c. sugar
2 egg whites
3/4 c. all-purpose flour
1 pinch of salt
1 tbsp. grated orange zest
2 tbsp. buttermilk or plain yogurt
1 tsp. vanilla extract

Preheat oven to 375 degrees. In a medium bowl beat the butter on high speed for 1 minute. Add sugar and beat until light and fluffy, about 2 minutes. Add the egg whites and beat until incorporated for 2 minutes.

Blend in the flour, salt and orange zest on medium speed until incorporated, about 15 seconds. Add the buttermilk and vanilla and continue beating until thoroughly blended, about 1 minute.

Drop round teaspoon of the dough onto a large, ungreased baking sheet, allowing 2 inches between each for spreading. Bake until the cookies are golden and brown around the edges, 10-13 minutes. Let cool on the baking sheet for about 2 minutes, then transfer to racks with a spatula and cool completely.