Make Raspberry Coulis at least 4 hours in advance: Combine raspberries, sugar and liqueur in a bowl and place in refrigerator; stir occasionally to dissolve sugar as raspberries thaw. After serveral hours, puree the ingredients (blender or food processor) and push through a fine mesh sieve. Discard seeds and solids. Refrigerate sauce (makes about 1 1/2 cups).
Mousse: Place Marsala and sugar in a saucepan; bring to a rolling boil and reduce to a syrup (about 10 minutes of boiling). Set Marsala syrup aside to cool.
Melt chocolate chips (this can be done in a microwave or in a double boiler).
Assemble mousse in food processor: start by blending ricotta and vanilla until smooth. Add Marsala syrup and melted chocolate; process until smooth. Add half of Cool Whip; process. Add other half and process gently to combine.
Place mousse in refrigerate to set for at least 2 hours.
To serve, place a pool of raspberry coulis on a plate and top with a scoop of mousse. Garnish with a mint leaf and fresh raspberry if desired.