Whisk the 2 envelopes of gelatin, brown sugar, espresso powder, and salt in a medium sauce pan. Add the milk while whisking and let sit 20 minutes. Heat over a medium flame while whisking, until the gelatin and sugar are dissolved, about 5 minutes. Do not bring to a simmer, just get it hot. Add the 4 cups of cream and mix well.
Pour through a fine mesh strainer into a 2 quart bowl or smaller containers. Chill for 8 hours, then cover and chill at least another 4.
To make the glaze, at least 1 hour before serving, heat the sugar, water and salt in a small sauce pan for 5 minutes or so, stirring occasionally, until the sugar is full dissolved. Cool to room temp and cover until ready to use. When ready to serve, pour a thin layer of the sauce over the top (you won't use it all) and sprinkle with salt if desired.