In a large mixing bowl, mix together the flour, butter and sugar until you have a nice mixture that resembles breadcrumbs. 

Add the egg and mix until the pastry dough holds together. 

Let the pastry dough rest in the refrigerator for 30 minutes. 

Lightly butter a 10-inch tart pan with a removable bottom 

Press the dough very firmly on the bottom and up sides of the tart pan.

With the tines of a fork, prick the bottom of the bottom of the tart pan. Place the tart pan in the freezer for 30 minutes until the pastry is hard.

Preheat oven to 400 F {R6 on the bottom shelf of an AGA eR7} 

To make the filling; in a large bowl, beat the eggs then add the cream, lemon juice, lemon zest, and sugar. Mix until smooth. Pour the lemon filling into the pastry pan. 

Bake the tart for 30 minutes.

Remove from the oven and place the tart pan on a wire rack to cool. 

Once cool, using a sieve, dust a little powdered sugar over the top.