In a food processor, (or mashing inside a plastic bag with a rolling pin or mug) pulse the chocolate wafers until finely ground, transfer to a mixing bowl.
In a small saucepan, melt the butter, then pour it over the ground wafers. Add a pinch of salt and mix with a rubber spatula or wooden spoon. Turn the mixture into to a 9-inch glass pie or baking dish. Press with your hands or a mug, to create a crust that covers the bottom and goes up the sides of the dish. Refrigerate for 20 minutes, or pop it in the freezer for 5 minutes, to form a firm crust.
Melt the chocolate in a double boiler. Set aside.
In a food processor, pulse the ricotta for a few seconds until fluffed up. Add the melted chocolate and puree for about 45 seconds more, until creamy and thoroughly mixed.
Using a whisk or fork, whip 1/4 cup of whipping cream in a large bowl until it thickens. Add the ricotta chocolate mixture to the whipped cream, stir it well to combine.
Remove the crust from refrigerator and spread the filling inside. Place it back in the refrigerator for a couple of hours before serving.