Preheat the oven to 350°F (180°C). Butter an 8-inch (20-cm) square baking dish or line it with parchment paper.
In a medium bowl, whisk together the almond meal, flour, coconut, salt, and baking powder.
In a separate bowl with a handheld mixer or in the bowl of a stand mixer, beat the softened butter with the brown and granulated sugars until light and fluffy, 2 to 3 minutes. Add the egg white and beat until well combined.
Add the flour mixture to the butter mixture and beat until combined, about 15 seconds. The dough will be pretty sticky. If you have time, you can cover and refrigerate the dough for about 15 minutes.
Dump half the dough over the bottom of the baking dish, using your fingers to press it into an even layer. (Buttering your fingers or using the wrapper from your stick of butter will help keep the dough from sticking to your fingers.)
Spread the jam over the surface of the dough, leaving a fraction of an inch or a half centimeter space between the jam and the pan so the bars won’t stick quite so much to the pan.
Top the jam with the remaining dough, using your fingers to make big crumbles of dough. The dough won’t cover the entire surface and that’s okay because some blobs jam left showing in between the crumbles is what makes this dessert so attractive.
Bake for 30 to 35 minutes, until the topping starts to turn deeply golden brown.
Let the jam bars cool in the pan and then cut into bars. The jam bars are best devoured the same day as the bottom crust tends to get a touch soggy if covered and kept overnight.