Preheat oven to 350°F. Add butter and chocolate chips to WildSide jar. Secure lid and select "Batter." Add eggs, cocoa, sugar, and vanilla to jar and secure lid. Press "Pulse" 3–5 times. Add flour and secure lid. Pulse 3–5 times, and use spatula to scrape down sides of jar.
Pour into greased 9-x-9-inch or 11-x-7-inch pan. Bake for 30 minutes or until wooden toothpick inserted in center comes out clean.
If you're a nut lover, fold 1 cup chopped walnuts or pecans into batter. If you're a chocolate lover, fold 1 cup semisweet chocolate chips into batter.