Warm up the milk chocolate and peanut butter over a double boiler until it reaches 104 to 133 degrees F. Add the corn syrup and sea salt. Emulsify with a rubber spatula, then use an immersion blender to obtain a smooth ganache. Reserve and use when it's between 86 to 80 degrees F.
Temper the dark chocolate by melting it to 140 degrees F, then cool over a cold water bath to 86 to 90 degrees F. Pour the tempered chocolate into the cavities of the mold, then flip the mold over the bowl of chocolate and tap to let the excess chocolate fall back into the bowl. Scrape the top of the mold clean, leaving only the thin shell of chocolate in the cavity. Allow to crystallize at room temperature for 1 hour (you can put in the fridge for 10 minutes to expedite the process).
Once the chocolate is set, fill the molds just below the top with the peanut ganache. Tap to settle, and allow to crystallize.
Once the ganache is set, seal the ganache with another thin layer of dark chocolate, making sure to scrape the mold so only the candy forms remain. This will allow them to come out easily.
Once the chocolate is set (ideally overnight), tap out the bonbons to release from the mold. (I like to put them in the freezer for 2 to 3 minutes before to help them to come out easily and more solid.)