To make the crust: In a food processor grind the walnuts and sugar together. Stir in the melted butter, cover and refrigerate for at least 1 hour, and up to 4 days. Using your fingers pack 1 1/2 teaspoons of mixture into small rings or collars 1 1/2 inches in diameter by 2 inches high. Bake for 7 minutes. Let cool slightly before adding filling.
Reduce the oven temperature to 300 degrees F.
To make the filling: In an electric mixer, with a whip attachment cream the cream cheese. Mix in the remaining ingredients in order. Pour into baked crust lined collars filling to about 3/8 inch from the top. Bake for 15 to 18 minutes, or until slightly puffed and barely shimmying in the center. Remove from oven and let cool a few minutes if puffed to make room for the creme fraiche topping.
To make the topping: Blend all ingredients and place 1 tablespoon on top of the each mini cheesecake. With a small off-set spatula or a teaspoon, ease the topping to coat evenly. It will level itself out during baking. Bake at 300 degrees F for 5 minutes. Cool to room temperature, then cover and chill at least 4 hours or up to 2 days. To serve, warm the rings and slip the cheesecakes out of them.