First - crush the salted pretzels - not too fine, but not too chunky either.
Mix the pretzels with all the butter and sugar. Press in the bottom of a 9x9 pan.
Next - mix up the 2 eggs, canola oil, and the whole box (not the chocolate pack) of marble cake mix - note, you're not following the directions on the box. Add in the peanut butter chips. Mix well. Set aside.
On top of the pretzel bottom, make a layer of butterfingers. Cover the whole area.
Top with 1/2 the cake mix.
Mix in the chocolate pack into the remaining cake mix. Mix well.
Top off the brownie with the chocolate cake mix.
Bake in the oven at 350 degrees for 30-35 minutes.
Let cool - then cut and eat.