Rub the bottom and sides of an 8” spring-form pan generously with butter.

In a small bowl, mix together the cookie crumbs, melted butter, brown sugar and vanilla.

Press into the buttered pan; set aside.

Place the half & half, cream, butter, egg yolks, sugar, cocoa powder and corn starch in a medium (heavy) saucepan.

Whisk vigorously while bringing the mixture to a gentle boil.

Add the sweet potatoes, sour cream and cream cheese, stirring constantly until the cream cheese has melted (about 6-8 minutes).

Remove from heat and stir in the chocolate chips; continue stirring until chocolate has melted and mixture is very smooth.

Pour into prepared pan and allow to sit at room temperature for 30 minutes.

Cover with tin foil and place in the freezer for 5-6 hours.

To unfold, remove from freezer 20 minutes before serving and cut into thin slices (this is a very rich dessert) and serve with whipped cream and berries.