Place your granulated sugar and lemon zest in a bowl. Use your fingers to rub the zest into the sugar for 2 minutes.
Cream the 'lemon sugar' and butter together until light and fluffy. Stir in the vanilla and 1 teaspoon of lemon juice.
Gradually add the flour and salt. Mix until the dough just starts to clump together.
Press the dough into a parchment-lined 8x8 inch baking pan (for 'fingers') or roll into a log. Chill for at least 30 minutes.
Bake at 160°C (325°F) for 25–30 minutes.
While still warm from the oven, sprinkle the top with a tablespoon of extra granulated sugar.