Line a 9x13-inch baking pan with parchment paper, leaving some overhang on the sides to help lift the bars out easily once set.
In a large mixing bowl, beat the softened unsalted butter and creamy peanut butter together with an electric mixer until smooth and creamy, about 2-3 minutes on medium speed.
Mix in the vanilla extract and kosher salt until fully combined to deepen the peanut butter’s richness.
Gradually add the powdered sugar, about a cup at a time, mixing on low speed to avoid a sugar cloud. The mixture should be thick and dough-like but pliable once all sugar is incorporated.
Transfer the peanut butter mixture into the prepared pan and press it evenly and firmly into the bottom with a spatula or your hands to create a smooth, compact layer.
Gently melt the chocolate chips with the refined coconut oil in a double boiler or microwave, stirring frequently until glossy and smooth without overheating.
Pour the melted chocolate over the peanut butter base and spread it evenly with an offset spatula or the back of a spoon.
Before the chocolate sets, sprinkle festive sprinkles evenly on top, if using.
Place the pan in the refrigerator for at least 2 hours, or until the chocolate is completely firm.
Use the parchment paper overhang to lift the slab from the pan. Cut into bars of desired size and serve. Store leftovers in the fridge.