1 teaspoon baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
1/2 cup butter, softened
3/4 cup sugar
1 egg
3/4 cup sour cream
1/2 teaspoon vanilla extract
2 cups rhubarb, diced
Preheat the oven to 350 degrees F. Line two baking sheets with parchment paper. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. In a large bowl, beat the butter and sugar together with an electric mixer at medium speed until light and fluffy. Add the egg and beat to combine. Beat in the sour cream and vanilla, making sure all the ingredients are well combined. Add 1/3 of the flour mixture and beat until combined. Add another 1/3 of the flour mixture and repeat until all the ingredients are combined. Stir in the rhubarb. Drop rough tablespoons of batter onto the prepared baking sheets, spacing them about 2 inches apart. Bake 10 to 12 minutes, until the edges of the cookies start to brown and the tops of the cookies get a little color. Let cool slightly, then remove to a rack to cool completely.