To make the Salted Chocolate Syrup: In a measuring cup combine 1/4 cup crushed dark chocolate , 1/4 cup crushed milk chocolate, and slowly stir in the hot water until you get the thickness you desire (should be more watery than thick).
Add salt, in parts, to taste.
Set a small amount aside in a shallow bowl or dish to rim the cocktail glasses. Store the rest in a covered refrigerator safe container or jar (use for ice cream and desserts if you like!)
Make the Simple Syrup
Add 1/2 cup hot water to 1/2 cup sugar, and stir until sugar dissolves completely.
Place in a refrigerator safe container and let cool to room temp. Store in the refrigerator when not in use.
Make the martini
Rim a chilled cocktail glass with some of the Salted Chocolate Syrup.
Combine vodka, vanilla, Salted Chocolate Syrup, heavy cream, and Simple Syrup in a shaker without ice and shake hard for 20 seconds. This is called a dry shake.
Add ice to shaker and shake hard again for ten seconds, just to chill the drink and add some froth.
Strain into the chilled (and syrup-rimmed) cocktail glass.