Preheat your oven to 350°F. Grease a 9x13-inch baking pan with cooking spray or line it with parchment paper.

Using a stand mixer or a hand mixer on medium speed, beat together the butter, peanut butter, and sugars until fluffy, about 2 minutes.

Add the eggs and vanilla extract, mixing for another minute on medium speed.

Gradually add the flour and salt, mixing on low speed just until combined, about 20 seconds.

Fold in the chocolate chips.

Pour the batter into the prepared pan and use a spatula to spread it evenly.

Sprinkle the peanut butter M&Ms on top, along with the optional googly eye sprinkles.

Bake for 25-30 minutes, or until the center is set but still soft. Note: If you're using a glass or smaller pan, you may need to adjust the baking time.

Once baked, optionally top the bars with the Halloween Reese's. Let them sit for about a minute to soften, then press two googly eye sprinkles onto each peanut butter cup.

Allow the bars to cool for about an hour before cutting into them. Enjoy your spooky treats!