Step 1: Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking pan or line it with parchment paper, leaving an overhang on the sides for easy removal.
Step 2: In a large mixing bowl, combine the cake mix, vegetable oil, and eggs. Stir until the ingredients are just well blended. If using, mix in the vanilla extract.
Step 3: Gently fold in the chocolate chips, pastel M&M’s, and sprinkles (if desired) until they are evenly distributed throughout the cookie dough.
Step 4: Press the prepared cookie dough evenly into the bottom of your prepared baking pan.
Step 5: Bake for 20-25 minutes, or until the edges are lightly golden brown and a toothpick inserted into the center comes out clean.
Step 6: Remove the pan from the oven and allow the cookie bars to cool in the pan for 10-15 minutes. This helps them set. Then, use the parchment paper overhang to lift them onto a wire rack to cool completely.
Step 7: Once completely cooled, cut the bars into squares or rectangles and serve. Enjoy your festive Easter treat!