Preheat the oven to 350°F (175°C). Line a 9×13-inch pan with parchment paper or lightly grease it.

Cream the butter and sugars together in a mixing bowl until light and fluffy, about 2–3 minutes.

Add the eggs and vanilla extract, then mix until combined.

Whisk together the dry ingredients in a separate bowl. Gradually mix this dry blend into the wet ingredients until just combined.

Fold in M&Ms, chocolate chips, and optional sprinkles.

Spread the dough evenly into the prepared pan, pressing it gently.

Bake for 20–25 minutes, or until the edges are golden brown and the center is set.

Cool completely before cutting into squares or bars.