Mix together flour, sugar and salt in a large bowl. Use a cheese slicer, if you have one, to slice the butter thinly – if not, you can simply dice the butter with a knife.

Add the sliced or diced butter to the dry ingredients, and using your fingers or a pastry cutter, cut in the butter until dough is crumbly but there are still some small visible pieces of butter.

Drizzle with ice water, 1 tbsp at a time, and mix gently with a fork until dough just comes together, do not knead the dough.

Form the dough into a ball and place it on a piece of plastic wrap.

Flatten into a disc, wrap in the plastic wrap and place in fridge for at least one hour but preferably overnight.

Let the dough rest for a few minutes at room temperature.

Roll out the dough into a large circle about 1/8 – 1/4 inch (3-5 mm) thick, on a lightly floured surface. Make sure to roll and turn the dough so it doesn’t stick to the surface.

Using the rolling pin, transfer the dough to a baking sheet covered with baking paper.

Slice the rhubarb into batons and place them in a bowl. Toss with the lemon zest, juice, granulated sugar and cornstarch.

Arrange the rhubarb batons in a decorative pattern on top of the dough, leaving a border around the edges. Fold the dough over the fruit and press gently to seal.