Step 1: Prepare the Batter

1. Preheat your oven to 350°F (175°C). Grease and line a 9×13-inch baking pan with parchment paper, leaving some overhang for easy removal.
2. In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
3. In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.
4. Beat in the eggs one at a time, followed by the vanilla extract, mixing until well combined.
5. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Fold in the M&M candies and chocolate chips if using.

Step 2: Bake the Cookie Bars

1. Pour the cookie batter into the prepared baking pan and spread it evenly.
2. Press a few extra M&M candies into the top of the batter for decoration.
3. Bake for 25–30 minutes, or until the edges are golden and a toothpick inserted into the center comes out with a few moist crumbs.
4. Remove from the oven and let the bars cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely.

Step 3: Slice and Serve

1. Once cooled, lift the bars out of the pan using the parchment paper overhang and cut into squares or rectangles.
2. Serve and enjoy these M&M Cookie Bars.