Refrigerate the dough for at least 30 minutes before baking to prevent excessive spreading and achieve those coveted crispy edges with chewy centers that define bakery-quality monster cookies.

Lightly toast the old-fashioned oats in a dry skillet for 2-3 minutes before adding to the dough to deepen their nutty flavor and add complexity that elevates the entire cookie.

Add extra M&Ms on top immediately after placing dough on the baking sheet (not before baking), so they set into the surface rather than sinking, creating that vibrant confetti appearance.

Use browned butter instead of standard softened butter to add a rich, nutty depth that complements the peanut butter and chocolate while creating more complex flavor layers.

Remove cookies when the centers still look slightly underdone (about 1-2 minutes before edges fully brown), as carryover heat will continue cooking them to perfect soft centers while edges crisp up.