In a large bowl, cream butter, cream cheese and sugar until light and fluffy. Add eggs, one at a time, beating well after each addition. Beat in vanilla.
Combine flour, baking powder, and salt; stir into creamed mixture just until moistened. Fold in cranberries.
Fill greased or paper-lined muffin cups three-fourths full.
Bake 20-25 minutes or until a toothpick inserted in the muffins comes out clean. Cool 5 minutes. Remove to cooling rack to cool completely.