Preheat oven to 350 degrees F with rack in center. Line 8x8-inch baking dish with parchment paper, leaving 2-inch overhang on sides for easy removal when done baking. Spray with cooking spray.

In large bowl, combine flour, baking powder and salt.

In mixing bowl with electric mixer, beat together sugar and butter until light and fluffy, about 2 minutes. Beat in eggs, one at a time, followed by sour cream and vanilla.

Gradually add dry ingredient mixture to wet ingredients, mixing on low speed until just combined.

Fold in cranberries with wooden spoon.

Transfer batter to prepared baking dish and spread into even layer. Bake 25-30 minutes, or until a toothpick inserted into center comes out mostly clean. Cool for 10 minutes in pan, then use the parchment paper to lift and remove cake from pan. Slice into squares to serve.