MAKE THE SHORTBREAD

1. Preheat oven to 350 degrees F. Line an 8×8″ metal baking pan with parchment (use a bit of butter to help it stick), leaving an overhang on all sides to aid in lifting the bars out.
2. In the bowl of a stand mixer (or a medium bowl using a hand mixer), cream the butter and brown sugar until light and fluffy, about 3 minutes.
3. Reduce the mixer speed to low and gently beat in the flour. Mix just until the flour is incorporated and the dough begins to form in clumps. 
4. Tip the dough clumps into the pan and press them evenly across the bottom of the pan. 
5. Bake at 350 degrees for 18-22 minutes, until the shortbread is lightly browned on the edges. Avoid over-baking, as it will make your shortbread layer overly crumbly.
6. Remove from oven and set aside to cool. Tip: You’ll need the hot oven for a future step, so I recommend leaving it on.

MAKE THE CARAMEL

1. In a medium pan set over medium-high heat, combine the sweetened condensed milk with 4 TB salted butter.
2. Stirring constantly, bring the mixture to a boil.
3. Reduce the heat to medium-low (if needed, raise the heat a bit to make sure the mixture is still bubbling gently) and continue to cook, stirring constantly, until the caramel is thick and a dark-golden shade of beige (about 7-10 minutes for me, could take a bit longer). I cannot overstate the need to stir constantly in order to avoid burning/overly browning the caramel. If you notice small brown flecks developing, that means the caramel is starting to brown on the bottom – reduce the heat immediately and keep stirring, stirring, stirring. 
4. Remove from heat and whisk in the vanilla extract.
5. Pour the caramel on top of the shortbread and spread it evenly with a silicone spatula.

ASSEMBLE THE REMAINING LAYERS

1. Immediately after you smooth the caramel, sprinkle the salted peanuts evenly on top, pressing them gently into the caramel to help them adhere. 
2. Sprinkle the peanut butter chips on top of the peanuts and return the pan to the 350-degree oven just for a minute or two, until the chips are melted enough to spread. Spread the chips in an even layer over the peanuts.
3. Allow the pan to cool, then refrigerate the layers for at least 45 minutes, up to overnight. If you’re in a hurry, you can also freeze it for 15-20 minutes. 
4. When the layers are firmly set, remove the pan from the refrigerator and, gripping the overhanging sides of the parchment paper, carefully lift the bars out of the pan.
5. Place on a sturdy cutting surface and, using a heavy sharp knife, cut into 36 small squares (you can also make larger bars if you wish). 
6. Return the bars to the refrigerator to keep them firm while you melt the chocolate.

COAT THE BARS

1. Using a double boiler, a heat-safe bowl set over a pan of boiling water (my preferred method), or simply a bowl in the microwave, combine the chocolate chips and the coconut oil and heat gently, stirring occasionally, until melted into a uniform, glossy, pourable consistency. Allow to cool slightly.
2. Set up a workspace:  I recommend lining a baking sheet with parchment, and placing it, along with the bars and the bowl of chocolate, on whichever side makes sense for your orientation (I’m right-handed, so I place the baking sheet to my right and the bars and chocolate to my left). 
3. Using two forks or a spoon, dunk one bar in the bowl of chocolate, ensuring it’s covered completely. Using one of the forks or the rim of the bowl, scrape the bottom of the bar to remove excess chocolate – this will allow for a cleaner finish with no chocolate puddling at the bottom. Set the chocolate-covered bar on the parchment. If you’re finishing with a sprinkle of flaky salt or chopped peanuts, add it now, before the chocolate sets. Repeat the process with the remaining bars. 
4. Refrigerate the bars until firm and fully set. If desired, you can melt additional chocolate or peanut butter chips to drizzle artistically on top of the bars. 

Store the bars in the refrigerator for up to two weeks. They can also be frozen for longer but may develop a “bloom” on the chocolate (totally harmless, but creates a white, cloudy cast).