Butter a 9" tart pan and refrigerate.  Combine all the ingredients for the pastry dough in a food processor and process until completely combined. Spread the mixture evenly over the bottom and side of your tart pan.  Chill for 30 minutes. Bake at 350 degrees for 12 minutes. Set aside to cool.

Combine the eggs and sugar in a metal bowl and place over a pot of just enough simmering water so that it does not actually touch the bottom of your bowl. Stir constantly until the sugar dissolves and the yolks thicken.  This takes about 20 minutes. Resist the temptation to turn up the heat as this will scramble your eggs. Slowly drizzle in the lemon juice while you continue to stir, maintaining the nice thick creamy consistency of your custard. Remove from the heat. 

Beat in the butter a tablespoon at a time.

Scoop the custard into the tart shell. Chill

Twenty minutes before serving, beat the heavy cream with 2 tablespoons of powdered sugar. Evenly spread the cream over the top of the tart. Serve immediately.