Start by warming up your oven to 350°F (175°C) to get it ready for baking.
Prepare a 9x13 inch baking pan by lining it with parchment paper, leaving an overhang on the sides for easy lifting, or simply give it a light spray with cooking spray for a non-stick finish.
In a medium saucepan, combine the softened butter and brown sugar. Gently heat over low to medium heat, stirring continuously until the mixture is beautifully smooth and melted. This step helps create that perfect chewy texture!
Take the saucepan off the heat and let the mixture cool down for about 5 minutes. It's important to let it cool slightly before the next step.
Carefully whisk in the eggs, one at a time, ensuring each is fully blended into the sugar mixture before adding the next. This creates a smooth base.
Stir in the vanilla extract. Then, gently add the flour, salt, baking soda, and baking powder. Mix just until everything is combined and no dry streaks of flour remain – be careful not to overmix to keep them tender.
Fold in half of the chocolate chips and half of the festive Valentine's M&M's into the batter. This ensures lovely bursts of flavor throughout each bar.
Spread the delicious batter evenly into your prepared pan. Then, sprinkle the remaining M&M's and chocolate chips generously over the top for a beautiful finish.
Bake in your preheated oven for 25 to 30 minutes, or until the edges are golden and a toothpick inserted into the center comes out with moist crumbs, not wet batter. Avoid overbaking to keep them soft and chewy.
Let the blondies cool in the pan for at least 30 minutes until they are just slightly warm. This makes them easier to cut cleanly into delightful bars. Enjoy this sweet treat in moderation!