Whisk the egg with the vanilla – just casually, by hand – then stir into the pan, giving a final little whisk, if needed, to make sure everything’s mixed together thoroughly, before folding in the nuts and chocolate chips. Pour and scrape this nubbly brownie batter into an aluminum foil pan measuring approx. 7 x 4 x 2 inches. Bake in the oven for 15–20 minutes until it is beginning to come away at the sides and the top has dried a little just around the edges.