• Preheat oven to 350℉. Grease your 9 x 13 and set aside.
• In a medium bowl, add whole milk and vinegar and stir to create buttermilk! Set aside and let rest for at least 5 minutes.
• In large bowl, whisk together flour, sugar, baking powder, baking soda, and salt.
• By this time, our buttermilk science experiment should be complete! To the milk, add melted butter, eggs, and vanilla. Give it a good beating to break yolks and combine.
• Add the wets to the dries and whisk until fully incorporated. Some lumps are ok. Let this sit while you complete the next step.
• Microwave jelly for 1 minute or until you can stir it and it becomes liquidy. Repeat with peanut butter.

ASSEMBLY!

• Grab your greased 9 x 13 and a spatula.
• Give the pancake batter a stir and add enough to just cover the bottom of the dish. Spread and level with spatula.
• Add HALF the jelly in row or blobs; it doesn't have to be pretty as this layer will not be seen. Repeat with HALF the peanut butter.
  
• Pour remaining batter on top. It's ok if the bottom pb&j peep through. Spread and level again with spatula.
• Carefully pour remaining jelly in parallel vertical or horizontal lines, from one side of the dish to the other. In the same direction, pour peanut butter next to the jelly. They do not need to be touching and this does not have to be perfect!
• Run a butterknife back and forth in opposite direction of the pb&j lines from one end of the dish to the other, creating the marbling effect.
• Bake on middle rack for 20-25 minutes (my exact time was 23 minutes, but every oven is different!). If you test with a toothpick, try not to hit the pb or j as it may look like wet batter.
• Allow to cool for 5-10 minutes before serving. Top with all the syrup!