The goal is to have diagonal lines drawn from a toothpick all over the pan, with lines that are about 1/2 even inches apart.
Take a toothpick and going 1/2 way down the brownie batter, starting from one corner of the pan (top left) to the adjacent corner (bottom right). Run toothpick across at 45 degree angles to make diagonal lines without pulling out the toothpick when reaching the edge of one side of the pan. (diagonal lines at the corner of the pan will be the shortest in length with the middle of the pan with the longest lines drawn.)
Without pulling out the toothpick reaching the edge of one side of the pan, circle around and at parallel 1/2 inch part from the first line, draw line through batter still at a 45 degree angle to the other side of the pan. Repeat through the entire pan until you reach the bottom right corner. See my pictures! I will do a video next time :) I love this leafy and even houndstooth-like swirl pattern!
Bake at 350 F for 30-38 minutes, remove from oven once the toothpick test in the centre of the pan doesn't come out runny. A little damp is fine. Cool completely before slicing! Enjoy!