For the topping:
Line a strip tart pan with tart dough and chill it for 2 hours, then prick the bottom well.
Preheat oven to 425 degrees F.
Meanwhile, with a paddle attachment cream the cream cheese until fluffy. Add the eggs one at a time, then, mix in the sugar, salt, and nutmeg. Add the lemon rind and juice and mix, then add the vanilla and cream at the end, on low.
Pour into the dough lined tart pan and bake, to slightly set the top. Mix the walnuts and sugar together. After baking for 10 minutes, sprinkle the top with the nut mixture and return to the oven for another 10 minutes. Turn the oven down to 350 degrees F and bake until the filling is lightly browned and slightly puffed, another 30 to 35 minutes.
Let cool to room temperature and serve or serve chilled.
In a mixer fitted with a paddle attachment, mix the flour and sugar. Add the butter and mix until coarse and sandy.
In a small bowl, whisk the egg yolk, 2 teaspoons cream, and vanilla together. Add to the flour mixture and mix at low speed just until combined. If the dough is not coming together when you squeeze it in your hand, add the additional 1 teaspoon of cream.
Turn out onto a work surface and form into a ball. Wrap in plastic wrap and refrigerate until ready to use.