Prepare the Cookie Dough:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper or lightly grease it to prevent sticking.

2. Mix Wet Ingredients: In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until the mixture is light and fluffy. This should take about 2-3 minutes using an electric mixer or a whisk.

3. Add Eggs and Vanilla: Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract.

4. Combine Dry Ingredients: In a separate bowl, whisk together the flour, baking soda, and salt. Slowly add the dry ingredients to the wet ingredients and mix until just combined. Be careful not to overmix, as this can affect the texture of the cookie bars.

Add the Fun Ingredients:

5. Stir in the M&Ms: Gently fold in the Easter M&Ms and any additional mix-ins like white chocolate chips or chopped nuts. Make sure the candy is evenly distributed throughout the dough, but don’t overwork it.

6. Transfer to Baking Pan: Spread the cookie dough evenly into the prepared baking pan. Use a spatula to smooth the top of the dough to ensure an even layer. Optionally, you can sprinkle a pinch of sea salt on top for added flavor and a slight contrast to the sweetness.

Bake the Cookie Bars:

7. Bake the Bars: Bake the bars in the preheated oven for 25-30 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean or with just a few moist crumbs. Be sure not to overbake, as you want the bars to remain chewy and soft in the middle.

8. Cool: Allow the cookie bars to cool in the pan for 10-15 minutes before transferring them to a wire rack to cool completely. This helps the bars set and makes them easier to cut into squares.

Cut and Serve:

9. Cut into Squares: Once the bars are completely cool, cut them into squares or rectangles of your preferred size. Serve immediately or store them in an airtight container.