Line a square 8x8-inch baking dish with parchment paper. Set aside.
To the bowl of a stand mixer fitted with the paddle attachment, beat the butter and peanut butter together on medium speed until well combined. Scrape down the sides of the bowl as needed.
½ cup unsalted butter, 1 cup creamy peanut butter
With the mixer on low speed, add the vanilla extract, then slowly add the powdered sugar.
1 teaspoon pure vanilla extract, 2½ cups powdered sugar
Once all of the powdered sugar has been added, allow the mixer to run on low speed until the mixture all comes together in a ball.
Transfer the peanut butter mixture to the prepared baking pan and pack it down, making sure to press it all the way to the edges. Set aside.
Add the chocolate chips and coconut oil to a small, microwave-safe bowl and microwave until melted.
2 cups chocolate chips, 2 tablespoons coconut oil
Pour the chocolate mixture over the peanut butter layer and use a spoon or offset spatula to push the chocolate into an even layer.
Transfer the bars to the fridge and allow them to sit until the chocolate has fully hardened, about 2 hours.
Slice the bars and top with flakey sea salt, if desired.