In a medium sauce pan over medium heat, bring 1 & 1/2 cups cream and mint leaves to a simmer. Remove from heat, cover with a lid and let steep 30 minutes.
Strain mixture through a fine mesh sieve into a bowl or glass measuring cup, to remove mint leaves. Set aside.
In the saucepan, whisk together vodka or water and gelatin. Let stand one minute to gel, then add strained cream mixture and mint extract. Return to medium heat and whisk until gelatin is dissolved and mixture is hot to the touch.
In a medium bowl, whisk egg yolks with powdered sweetener. Slowly whisk in about 1 cup of the hot cream mixture to temper yolks, then slowly whisk egg yolks back into hot cream. Whisk until mixture thickens slightly and reaches about 160F on an instant read thermometer.
Remove from heat, and whisk in green food colouring, if using. Refrigerate until cool and thickened to a pudding-like consistency, about half an hour, whisking every few minutes to avoid clumps.
Meanwhile, in a large bowl beat remaining cream to stiff peaks. When mint mixture is cool, gently fold into whipped cream to combine.
Spread in prepared crust and refrigerate until set, about 3 hours. Garnish with more whipped cream and chocolate shavings, as desired.