Preheat the oven to 350˚F and line a 9x13 casserole dish with parchment, leaving some overhang on the side for easy removal.
Place the butter and sugars in the bowl of an electric mixer fitted with the paddle attachment. Beat on medium speed until the mixture is very light in color, about 3 to 4 minutes. Use a rubber spatula to scrape down the sides of the bowl.
In a separate bowl, whisk together the flour and salt. Add the dry ingredients to the butter mixture and mix on low just until combined - its ok for it to look crumbly but it should hold together when pinched.
Separate out about ⅓ of the mixture and put into the freezer while you press the rest of the dough into your prepared pan. If the dough is sticky, chill it in the fridge for 10 minutes or use another piece of parchment to press it out.
Spread the jam in a thin even layer over the dough, leaving a ½ inch border at the edge.
Remove the dough from the freezer and crumble it over the jam along with the almonds.
Bake for 30-40 minutes, until the top is golden brown. Cool completely before slicing into squares.
Store at room temp, wrapped in plastic wrap, for 3-4 days.
This can be made up to 1 month in advance - following steps through assembly, wrapping it in plastic and placed in the freezer. Bake time should be about the same straight from the freezer.
Notes
*I made a cranberry + quince jam for mine which was delicious (see details below) but you can use any kind or flavor jam you like.
Recipe by Eat Some Wear Some at https://eatsomewearsome.com/fregolotta-a-shortbread-jam-situation/