These make a lot, so it takes some time for just two people to eat them if you’re trying to excercise moderation. However, we decided that we actually like them better after the flavors of the individual layers have had a chance to meld together. 
As is often the case when trying new recipes, we did have to make a last-minute trip to the store for a single ingredient. Surprisingly, this time it was for the proper size pan! We actually measured our jelly roll pans and discovered we had the 13×18″ size. That explains the mystery of why I often had trouble making batter spread far enough when making other bar cookies. 
Toffee Brownie Bars

3/4 c. butter, softened
3/4 c. firmly packed brown sugar
1 egg yolk
3/4 tsp. vanilla
1 1/2 c. all-purpose flour
1 pkg. chewy fudge brownie mix (about 18 oz.)
1 egg
1/3 c. water
1/3 c. vegetable oil
12 oz. pkg. chocolate chips, melted
3/4 c. finely chopped pecans

Preheat oven to 350 degrees. Grease 15 1/2 x 10 1/2 x 1 inch pan.

For crust, combine butter, brown sugar, egg yolk, and vanilla. Stir in flour. Spread in pan. Bake 12 minutes.

For filling, combine brownie mix, egg, water and oil. Spread on hot crust. Bake for 15 minutes. Cool for 30 minutes.

For topping, spread melted chocolate on brownie layer and garnish with pecans. Cool completely.