• Preheat the oven to 180 °C (350°F) (conventional setting).
• Weigh the ingredients. In a bowl, combine the dry ingredients and mix. Add the butter in small pieces, then rub it in with your fingertips to avoid overheating it. At first, the dough will seem crumbly, as if it needs an egg yolk or milk. Give the butter time to bind everything together; trust the recipe.
• Let the dough rest for a few minutes at room temperature (read the tips first).
• Line a baking pan with wet, wrung-out parchment paper; use your fingers to spread ¾ of the dough over the bottom, taking care to form the edges.
• Spread the jam over the bottom of the cake.
• Crumble the remaining dough evenly over the cake surface, as if making a crumble.
• Bake for 35 minutes in a preheated oven.
• Let cool before serving.

Tips

• Usually, shortcrust pastry dough needs to rest in the refrigerator before being rolled out. In this case, that's not necessary; you can use the dough right away as long as 1) the butter hasn't been worked for too long and doesn't need to be chilled, or 2) it isn't very hot (in your kitchen or outside the kitchen). In these cases, if the dough needs to rest, preheat the oven before you roll out the crust.
• Store outside the refrigerator for a few days.