
Line a 9×13 baking dish with parchment paper to prevent sticking.
In a large mixing bowl, use a mixer to beat 8 tablespoons of softened salted sweet cream butter until it's smooth and creamy.
Add 3 cups of creamy peanut butter and 2 teaspoons of pure vanilla extract to the bowl, mixing until fully combined.
Gradually incorporate 4 cups of powdered sugar, mixing until the mixture is smooth. The consistency should be thick yet spreadable.
Spread this mixture evenly across the base of the prepared baking dish, creating a flat layer.
In a microwave-safe bowl, combine 12 ounces of semi-sweet chocolate chips and 2 tablespoons of vegetable oil.
Heat the mixture in the microwave on medium heat in 30-second intervals, stirring in between, until completely melted and smooth.
Once melted, gently spread this ganache over the peanut butter layer in the baking dish, ensuring an even coating.
Place the baking dish in the refrigerator and chill for about 15-20 minutes, allowing the chocolate to firm up.
After chilling, remove the baking dish from the fridge and slice the bars into 15 squares, each measuring approximately 2½ in x 3 in.
Return the sliced bars to the fridge for an additional 1 hour and 45 minutes to ensure everything sets properly.
Once completely chilled, carefully lift the bars out of the dish using the parchment paper, slice again if necessary, and serve cold.