In a food processor, grind the pecans and sugar until the nuts are very fine. Sift together the flour, baking powder and cinnamon. In a medium bowl, using an electric mixer, beat the butter with the pecan mixture until light and fluffy. Add 2 of the eggs and the vanilla and beat until smooth. Using a wooden spoon, stir in the dry ingredients in 3 batches, mixing until the flour is incorporated; the dough will still be sticky.