1. Preheat oven to 350°. Line a 8x8 baking pan with parchment paper and set aside.
2. In a microwave safe bowl, heat butter in microwave until completely melted.
3. With a spoon, stir in brown sugar until smooth.
4. Add in egg and vanilla until combined.
5. Incorporate the flour and mix until just combined.
6. Fold in m&m's and chocolate chips (or other candy being used) until evenly distributed.
7. Spread mixture into prepared baking pan and make sure top is level. Place in oven and bake for 23-25 minutes. (Mine were done in 23 minutes.) They will appear to be not done, but trust me they are. They will firm up as they cool and be nice and chewy.
8. Once done, let them cool in pan for about 10 minutes. Pul them out by the parchment paper hanging over the sides and let them cool another 10 minutes. Cut them up into bars and enjoy!