In a large pitcher, stir together the tequila, Kahlua, espresso and half & half. Cover and refrigerate until chilled.
Moisten the rims of the martini glasses with water. Mix together the ground espresso and chocolate on a small plate, then upend the glasses into the mixture to crust the rims. Fill a cocktail shaker about 3/4 full of ice and add half the tequila mixture. Cover and shake for about 15 seconds to thoroughly chill the mixture. Strain into the prepared glasses. Repeat the process for the remaining tequila mixture.