01 - Line an 8x8-inch baking dish with parchment paper, leaving enough overhang on the sides to lift the bars out later.
02 - In a saucepan over medium-low heat, combine the peanut butter and maple syrup. Stir continuously until smooth and warmed through, about 2 to 3 minutes. Remove from heat and stir in the vanilla extract and sea salt.
03 - Gently fold the lightly crushed cornflakes into the peanut butter mixture until every piece is evenly coated.
04 - Transfer the mixture to the prepared baking dish and spread it evenly, pressing down firmly with a spatula. Place the dish in the freezer for 20 to 30 minutes until the layer is completely firm.
05 - Remove the set slab from the pan using the parchment overhang and cut it into 16 even bars using a sharp knife.
06 - Combine the dark chocolate chips and coconut oil in a microwave-safe bowl. Microwave in 30-second intervals, stirring between each, until the chocolate is completely smooth and glossy. Alternatively, melt using a double boiler over simmering water.
07 - Dip each bar into the melted chocolate, turning to coat all sides evenly. Lift out with a fork, allowing excess chocolate to drip off, and place on a parchment-lined tray.
08 - Refrigerate the coated bars for 15 to 20 minutes, or until the chocolate shell is fully hardened and set.
09 - Transfer the finished bars to an airtight container and store in the refrigerator for up to 2 weeks, or freeze for up to 3 months.