01 -
Heat your oven to 350°F and either grease a 9x13 inch metal baking pan or line it with parchment paper for easy removal.
02 -
Using an electric mixer, beat the softened butter with both sugars for about 2 minutes until the mixture becomes light and fluffy in texture.
03 -
Beat in the eggs one at a time, then mix in the corn syrup and vanilla until everything is well combined and smooth.
04 -
Mix in the peanut butter until fully blended, then stir in the baking soda and salt until evenly distributed.
05 -
Gently fold in the flour and oats, mixing just until the ingredients come together - don't overmix or the bars will be tough.
06 -
Stir in 3/4 cup of the chocolate chips and 3/4 cup of the M&M's, saving the remaining 1/4 cup of each for the festive topping.
07 -
Drop spoonfuls of the sticky dough into your prepared pan and gently spread it smooth. Sprinkle the reserved chocolate chips, M&M's, and all the sprinkles on top, pressing them lightly into the surface.
08 -
Bake for 28-32 minutes until the edges are golden brown and the center looks set but not wet. Don't overbake - you want these soft and chewy!
09 -
Let the entire pan cool completely on a wire rack before cutting - this prevents crumbly, messy squares. For the cleanest cuts, chill the pan briefly before slicing into 12-24 squares.