In a medium-sized saucepan, sprinkle the gelatin over the cooled espresso and let stand about 1 minute to soften.
Heat the gelatin mixture over low heat until the gelatin is dissolved. Add the cream. Heat over medium heat for 1 minute.
Remove from the heat and allow to cool for 10 minutes before stirring in the mascarpone, sweeteners, extracts and salt. Taste and adjust sweetness to your liking.
Divide the panna cotta among 6 martini glasses or ½-cup ramekins and cool to room temperature. Chill, covered, for at least 4 hours or overnight.
Served dusted with unsweetened cocoa powder or drizzled with sugar free chocolate syrup, if desired.