Allow butter and cream cheese to soften by setting out at room temperature for 30 minutes.  Preheat oven to 350 and lightly grease a baking sheet. 

Combine butter, cream cheese, and sugar in a large bowl, and cream together with a hand mixer.  Add in egg and vanilla extract, and mix until incorporated. 

In a medium bowl, combine flour, baking powder and salt. Add the flour mixture, 1/2 cup at a time, to the cream cheese mixture, beating well after each addition, until all fully mixed. 

Divide out cookie dough into tablespoon-sized spoonfuls, and roll into small balls and place onto baking sheet, leaving enough room between each cookie. 

Bake in preheated oven for 8 - 10 minutes, or until cooked through.  Transfer to a wire rack and allow to cool.