Make the chocolate sauce: In a pot, cook together the salt, butter, sugar and milk until the sugar dissolves. Remove from heat and add the chocolate and vanilla, stir. You can make this ahead of time and store it in the fridge for up to a week. You’ll want to warm it just until it’s at room temperature before serving over the pavlova. Don’t pour it over hot, it will melt the whipped cream.
Make the pavlova: Draw a 6 or 8 inch circle on parchment paper then flip the paper over and set it on a cookie sheet. Have a mini spatula ready. Preheat the oven to 275 F (if your oven runs hot do 250 F).
Bring a pot filled ⅓ high with water to a simmer. In a heatproof bowl that will fit on top of the pot (but not touch the water) whisk together the egg whites and sugar. Set it over the heat whisking non-stop until you can pinch it and feel no sugar granules.
Transfer the egg mixture to your stand mixer bowl and begin whipping on low then gradually speed it up until it’s at medium high. Whip until you have stiff peaks, about 10 minutes - right before the stiff peaks stage add the vanilla, vinegar and cornstarch (one at a time and carefully so as not to deflate it).
Carefully dollop the meringue onto the prepared parchment paper. Use the offset spatula to shape it into a dome, sliding upwards to create a pretty pattern and pressing down in the top center to create a ‘well’. Use a wet finger to clean the bottom of the meringue.
Bake the pavlova for an hour then reduce the heat by 25 degrees and bake for another hour or until the pavlova seems set. It’s okay if it has cracked! Turn the oven light on and shut off the oven. Leave the pavlova in there overnight, or at least four hours until you are ready to assemble.
Make the whipped cream: Beat together all the ingredients until you have medium peaks, about 3-5 minutes (use a hand mixer or if you are feeling like a workout, use a whisk). Stop before you get to ‘stiff’ peaks as this will be too close to butter! Alternatively, (and this is a new favorite method of mine) put all the ingredients in a food processor and process on high until you have a thick cream - a few minutes.
Assemble the chocolate sauce pavlova: Remove the pavlova from the oven and dollop the whipped cream into the center, filling it. Spoon the room temperature chocolate sauce over the top and sprinkle on the nuts and chocolate curls. Serve asap! Leftovers can be stored in the fridge but the pavlova might get a bit gummy.