how do I cook two boxes of brownie mix in 13x9 pan

You ask a great question!  Here are the directions for baking any two boxes of our Betty Crocker Premium brownie mix in a 13 x 9" pan.  Happy baking!  

Heat oven to 325°. 

Grease bottom of 13x9x2-inch rectangular pan. 

Prepare batter using 2 packages any Betty Crocker®Premium brownie mix, double all ingredients for the water, oil and eggs called for on the package directions.   

Bake 51 to 53 minutes for shiny metal or glass pan and 45 to 47 minutes for dark nonstick pan. 

Cool 1 hour before cutting.