Preheat the oven to 350 degrees.

Combine the flour, cocoa powder, baking powder and salt. Set aside.

In a microwave safe bowl, melt the butter and chocolate in 15-20 second increments, stirring until completely melted. Let cool 2-3 minutes.

In another bowl, combine the eggs, sugar and vanilla. Add in the melted chocolate mixture and then slowly add in the flour and cocoa mixture. Mix well and set aside.

Add 1 Oreo sandwich cookie to the bottom of each jelly jar.

Next, add 1/8 C. of brownie batter on top. Add another Oreo and then another 1/8 C. of brownie batter. You want the brownie batter to come up right under the jars ring. You don't want to overfill though as it will spread when baking.

Bake 20-25 minutes. Around 20 minutes insert a toothpick into the center of the brownie. If it comes clean, they are done.