Grease an 8 x 8 inch baking pan with baking spray or butter and set aside.
In a large bowl mix sugar with salt and set aside.
Add butter to a medium bowl and microwave for 1 minute, until melted.
Pour the butter over the salt and sugar, mix until combined. Whisk in the egg and mix until fully combined, the mixture should be thicker now and shiny.
Using a spatula, stir in the flour and mix just until incorporated. The dough will be very thick, almost like play dough. This is ok, if needed use your hands to incorporate last bits of flour.
Divide the dough in half, and press half of the dough into the bottom of the greased pan. Level it with the bottom of a measuring cup.
Pinch the dough with a fork and bake for 15 minutes.
In the meantime work on the cheesecake.
Add cream cheese and sugar to a medium bowl and using a mixer cream until light and fluffy.
Add the egg and lemon zest, whisk until fully combined.
Stop, and with a spatula scrape the sides and bottom of the bowl, mix again on medium-high speed until fully combined and no lumps are visible.
Combining all the layers:
After 15 minutes of baking, remove pan from oven, top the shortbread layer with the cheesecake batter. Using a spatula distribute it evenly. Work quickly as the cheesecake starts to melt from the heat coming from the shortbread layer.
Using a spoon, spoon the lemon curd on top of the cheesecake layer.
Same with the lingonberry jam, spoon it on top of the lemon curd cheesecake layer.
Crumble on top the remaining dough, pressing it slightly. You can use all the remaining dough or you can use less if you don't want the crumb mixture to be very thick.
Bake for 30 minutes or until the top is golden brown.
Cool completely to room temperature on a wire rack, after that transfer the pan to the fridge for at least 4-5 hours before slicing, if you want the bars to crumble less.