Preheat oven to 350 degrees F (175 degrees C). Lightly grease cookie sheets.
In a medium bowl, cream together the butter, brown sugar and white sugar until smooth. Stir in the egg and vanilla. Sift together the flour, baking powder, baking soda and salt, stir into the creamed mixture. Finally, stir in the rolled oats, white chocolate chips and pecans. Drop by tablespoons onto the prepared cookie sheets.
Bake for 10 to 12 minutes in the preheated oven. Remove from baking sheets to cool on wire racks.