Position a rack in the center of the oven and preheat to 350°F/175°C. Place butter, sugar, and vanilla in a bowl, and mix with a rubber spatula just until combined. It’s ok if there are still some small visible chunks of butter. Add the flour and mix with your hands until the dough comes together (some remaining crumbs are okay).

Take about two thirds of the dough, and press it evenly on the bottom of a 9-inch square baking pan. The dough layer will seem thin, but as long as it’s about ⅓-inch/8mm, that’s enough. Spread two thirds of the jam on top of the dough in the pan, leaving a ¼-inch/6mm border. Then spread the diced strawberries on top of the jam in a single layer. Spread the remaining jam on top of the strawberries. Break up the remaining dough into crumbles and sprinkle on top.

Bake for 40-45 minutes until lightly golden on top. Cool, slice into 12 bars, and enjoy! (We find these are great warm, but also delicious the next day after storing in the fridge in an airtight container).