Mix together cake mix, melted butter, and 1 egg. Blend for 1 to 2 minutes. The batter will be very thick - more like cookie dough. Reserve 2/3 cup of batter.
Pat remaining batter in bottom of 13x9 inch pan.
Bake for about 15 minutes or until crust is light brown and puffs up. Remove from oven and cool on a rack for 10 minutes. Leave the oven on.
Mix together reserved batter, corn syrup, brown sugar, remaining 3 eggs, and vanilla. Blend on low for 1 minute. Scrape down sides of bowl with a spatula. Mix at medium speed until well combined and blended. There will first be little chunks of the cake mix batter. Mix well until those chunks disappear.
Fold in pecans and chocolate chips.
Pour mixture on top of partially cooked batter and smooth it out with a spatula. Return pan to oven.
Bake cake until edges are brown but cetner is still a bit soft - 40-45 minutes.
Remove from oven and cook on a rack for 30 minutes.