Prepare the pan

1. Preheat the oven to 350° F (175° C). 

2. Line a 9x13-inch baking pan with parchment paper, leaving some overhand for easy lifting later.

Make the dough

1. In a bowl, combine flour, sugar, salt and lemon zest.

2. Add the cold butter and rub into the dy ingredients with your fingertips until the mixture looks sandy, with some small pea-sized pieces remaining.

3. Add the egg and vanilla and mix gently until the dough forms soft clumps. Do not overmix.

Form the base

1. Press about two-thirds of the dough firmly and evently into the prepared pan to form the base.

2. Place the pan in the refrigerator and chill for 10 minutes. This helps the base hold its shape during baking.

Add the jam

1. Warm the jams slightly so they spread easily.

2. Spoon the jams over the chilled base, placing them side by side. Use a spoon or offset spatula to spread gently. If desired, make one or two light swipes where the jams meet, but keep the colors most distinct.

Add the crumb topping

1. Crumble the remaining dough loosely over the jam layer

2. Do not press it down - the topping should stay light and uneven, with some of the jam visible.

Bake

1. Bake for 25-30 minutes, until the edges are just beginning to turn golden, the center still looks pale andsoft, and the jams appears glossy rather than dry.*

2. Do not wait for the center to look fully set - it will firm up as it cools. These bars are ment to be pulled early for a soft, jammy texture. 

*Ovens vary. Start checking early and trust how it looks rather than the timer.