To make the lavender sugar: layer lavender and sugar in the jar. Seal the jar and leave to infuse for two days before using.

To make the pastry: Sift the flour into a bowl. Rub the butter into the flour until it resembles fine breadcrumbs. Mix in the sugar. Add the water to the egg yolk and mix well. Add to the flour mixture. Bind together, adding a little more flour if the pastry seems sticky.  Shape the dough into a ball, flatten it slightly and wrap it in parchment. Leave in the fridge to rest for at least 30 minutes. Flour the surface and roll out the pastry until 3-5 mm/max 2 inches thick. Drape the pastry over the rolling pin to lift it over the tart tin, then unroll the pastry into the tin. Press the pastry into the bottom and up the sides, then press the pastry up slightly over the edge.

For baking the tart blind: Line the case with parchment paper and fill with baking beans. Bake for 15 minutes approx. in a preheated oven of 190°C/375° F /fan 170°C / 330°F /Gas 5, until pastry is just cooked. Remove the beans and lining. Brush with egg wash, return to oven for a further 2-3 minutes.

To make the filling: Grate the zest of the lemons and squeeze enough juice to give 250ml / 8½ fl oz. Break eggs into a bowl, add both of the sugars and whisk until combined. Add the lemon juice and zest. Add the cream and whisk lightly. Spoon off any large air bubbles and discard.

Pour the mixture into the partially baked pastry case. Bake for 20 - 25 minutes or until the tart is set and feels springy in the centre. Let it cool for ½ hour if you want to serve it warm. It is also extremely good chilled, dusted with icing sugar and decorate the edge with sprigs of mint and lavender flowers. Dust the centre with icing sugar. 

Tip: When pouring the lemon mix into the pastry case – pour the mixture into a jug first and then pour directly into the tart base whilst it’s in the oven – you will avoid a mess!