In a small sauce pan combine all ingredients except heavy cream and sour cream. Bring to a gentle boil white constantly whisking to dissolve the gelatin. Set aside.
In a bowl of a stand mixer whip the cream on high until peaks form.
Add sour cream and mix until well combined. Set aside.
Using a fine sieve pour the gelatin mixture into bowl with the whipped cream mixture, the sieve will catch the pieces of gelatin that did not dissolve.
Turn the mixer to medium and whisk until combined, the mixture will be thin but don't worry it's exactly like it needs to be.
Carefully pour the coffee mousse into either individual cups or an 9 inch round glass pan and place in the refrigerator for a couple hours. Dust with cocoa powder or decorate as desire (shaved chocolate or cocoa nibs)