Lightly grease a 9 x 13 inch baking pan with butter or nonstick spray. Line the bottom and long sides with parchment paper, allowing for an overhang for easy lifting. Spray the parchment with some grease.

Preheat your oven to 350°F (175°C) and adjust the rack to the center position.

In a large mixing bowl, whisk together the melted butter and creamy peanut butter until smooth. Add both sugars and whisk until thick and glossy. Crack in the eggs, whisking thoroughly after each addition, and stir in the vanilla extract.

In a separate medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and fine sea salt.

Gently add the dry mixture into the wet mixture and fold until just combined, careful not to over-mix.

Sprinkle the semi-sweet and white chocolate chips over the dough and fold them in until evenly distributed.

Spoon the dough into the prepared pan and press it evenly into all corners, leveling off the top.

Press half to two-thirds of the Valentine-colored M&M’s into the surface and sprinkle with Valentine sprinkles if desired.

Bake for 18 to 24 minutes, checking at 18 minutes for lightly golden edges and a slight jiggle in the center.

Press any reserved M&M’s into bare spots immediately after removing from the oven.

Allow the bars to cool completely on a wire rack for at least 1 to 1½ hours. Chill for extra fudginess if desired.

For an optional drizzle, combine white chocolate chips and neutral oil in a microwave-safe bowl. Heat in 15–20 second bursts until smooth and drizzle over cooled bars.

Lift the cooled bars from the pan using parchment and cut into squares or rectangles.

Store bars in an airtight container at room temperature for up to 3–4 days.