In a stand mixer fitted with the whisk attachment, combine the egg whites and salt.
Beat the whites until foamy, about 1 minute.
With the mixer running, add the espresso powder.
Slowly add the sugar and beat until firm with stiff, shiny peaks, about 3 more minutes.
Sift the cornstarch onto the egg whites and fold it in with the vinegar and vanilla.
Divide the meringue into 6 large mounds on a baking sheet.
Use the back of the spoon to create a small well in the middle of each glob.
Bake the pavlovas until they're hard on the exterior but still soft on the inside, about 1 ½ hours. Turn off the oven and leave the pavlovas in until cool, about 2 more hours, or overnight.
Meanwhile, heat half the cream to a simmer.
Add the ground coffee and remove from heat.
Let steep for 20 minutes then strain and chill.
Whip the infused cream with the remaining cream until soft peaks form, about 5 minutes.
When ready to serve, spoon 2 to 3 tablespoons of caramel sauce into the well of each pavlova.
Pipe or spoon the whipped coffee cream over the caramel.
If desired, dust cocoa powder over the top of the cream.