Heat oven to 350. Spray a 9" x 13" baking pan w/ cooking spray. In lg bowl, mix together flour, baking powder.
In another lg bowl, beat butter until fluffy, Slowly beat in sour cream, then sugar. Beat in eggs and vanilla. Fold into flour mix, mix well, but don't overmix.
In medium bowl, mix together brown sugar, pecans and cinnamon. Stir in melte butter until crumbly. Pour batter into pan, sprinkle w/ pecan mix. Bake 30 mins, or until a toothpick inserted in center comes out clean.