In a large mixing bowl beat butter and shortening with an electric mixer on medium to high speed for 30 seconds. Add brown sugar, baking powder, and baking soda. Beat until combined, scraping sides of bowl occasionally. Beat in egg and vanilla until combined. Beat in as much of the flour as you can with the mixer. Using a wooden spoon, stir in any remaining flour. Stir in the rolled oats, chopped chocolate, and 1/2 cup of the crushed peanut brittle.
Drop dough by rounded teaspoon 2 inches apart onto the prepared cookie sheets. Flatten each mound slightly.
Bake in a 350 degree F oven for 8 minutes. Remove cookie sheet from oven. Sprinkle with remaining 1/2 cup crushed peanut brittle, carefully pressing in slightly. Bake for 4 to 5 minutes longer or until edges are lightly browned. Cool on cookie sheet for 2 minutes. Transfer cookies to a wire rack; cool. Makes about 24 cookies.