Add the flour, sugar and salt to the bowl of a food processor and pulse to mix well. Add the cold butter and blitz for about 20 seconds until it starts to look like breadcrumbs. Add the egg yolks and blitz for another 10 seconds or so until well distributed (notes if you have no food processor).
Shape the dough into a ball, wrap in a piece of baking paper and sit in the fridge for 1/2 hour to chill.
Preheat the oven to 180C / 350F / 160C fan forced. Line the base of a 25cm (9inch) fluted tart tin with baking paper.
Once chilled, roll out the pastry between 2 sheets of baking paper to about 3-4mm thick. Remove the top sheet of paper and use the bottom sheet to help you flip the pastry over into the prepared tin, then remove the paper. Gently press the dough into all the corners and make sure the top edges are even. Prick the base all over with a fork.
Line the tart case with the same piece of baking paper and fill with baking beads (or rice). Bake for 15 minutes. Remove the baking paper with baking beads and return to the oven for another 15 minutes until golden.
Once cooled, spread jam over the base
To make the strawberry mousse
Purée together the strawberries and sugar then strain into a saucepan to remove most of the seeds. Discard seeds.
Sprinkle the gelatine over the strawberry puree then stir over low heat until the gelatine has dissolved. Place in the fridge for 1/2 hour to cool.
Whip the cream to soft peaks. Mix half a cup of the cream into the strawberry mix. Now gently fold the rest of the whipped cream through the strawberry being gentle so you don’t lose all the air you whipped into it.
Gently spread the mixture over the tart base. Place in the fridge for at least 2 hours to set.
For best results, you should always weigh ingredients like flour and sugar. Kitchen scales are relatively cheap but if you can’t weigh the ingredients, use the spoon and level method (don’t scoop).