Beat egg yolks, 1 tbsp maple syrup, and 2 tbsp sugar until thick and lemon colored.
Whisk the egg whites and 2 tbsp sugar (if not using pasteurized eggs) over a double boiler, stirring often. The bowl should not be touching the simmering water underneath. Heat until 140-145 for 15 seconds.
Remove from the burner and immediately pour the egg whites into a clean, cool bowl to cool. Stir often.
Melt chocolate over a double boiler with coffee extract or espresso, rum, water, and 1/2 tbsp maple syrup. The bowl should not be touching the simmering water underneath. Add the egg yolk mixture and stir to combine.
Heat the mixture over the double boiler to 145 degrees for 15-20 seconds (if not using pasteurized eggs.) Stir often. Set aside to cool.
When the egg white mixture is cooled to just barely warm or lukewarm, beat the mixture with the cream of tartar using a stand mixer or hand mixer on medium low speed until fine bubbles form.
Gradually dd 1 tbsp sugar and beat on medium or medium high speed until soft peaks form. Do not over whip. Fold into the chocolate mixture in thirds.
In a clean and dry bowl, whip cream until lines begin to form. Add 1 tbsp sugar and vanilla and beat until soft and pillowy.
Reserve 3/4 cup whipped cream to decorate the tops of mousse.
Fold in remaining cream into the chocolate mixture being careful not to overfold. Spoon into ramekins or glassware. Add cream piped or scooped on top. Refrigerate for 3-4 hours covered before serving. Top with chopped nuts, berries or cherries, or chocolate shavings just prior to serving.