Preheat oven to 350° F, and line an 8x8 baking dish with aluminum foil, being sure to let the ends of the foil hang over the sides of the baking dish (this will help lift the entire pan of bar cookies out of the dish after baking). Spray the foil (bottom and sides) with non-stick cooking spray.
In a medium sized bowl, mix together melted butter and brown sugar with a spoon until blended. Add egg and vanilla extract; stir well, until combined.
Add flour, baking powder and salt to the batter. Stir. Add assorted chocolate chips. Stir batter until ingredients are fully blended.
Spread batter into prepared baking dish. Bake at 350° F. for 20-25 minutes, or until top is golden brown and set. You can also test for doneness by inserting a toothpick into middle top of the bar cookies. If it comes out clean with no dough on it, they are ready! Since oven temperatures vary greatly, I recommend checking them at 20 minutes, then bake a few minutes longer, if necessary, to ensure they are baked through.
Once done, remove dish from oven; place dish on wire rack and let bars cool for 10 minutes. Using the foil overhang, carefully lift the entire pan of bar cookies out of dish and place (still on the foil) onto wire rack to finish cooling. Once cooled completely, cut into 12 equal sized squares. Serve, and enjoy!
If you can't find cinnamon chips at your store (sometimes they're seasonal), you can substitute butterscotch or peanut butter chips.
Triple Chip Bar Cookies https://www.thegratefulgirlcooks.com/triple-chip-bar-cookies/