In a medium mixing bowl, whisk together the flour, almond flour, and salt. Set aside.
In the bowl of a stand mixer, beat together the butter and sugar on medium-high speed for 2 minutes, scraping down the sides of the bowl as needed. Add the egg and vanilla and mix just until combined.
Turn the mixer to low speed and slowly incorporate the dry ingredients. Then, mix for about 2 minutes until well combined.
Place the cookie dough onto a large piece of plastic wrap and flatten it into a disk shape that's about 1 inch thick. Wrap to seal the dough, and then place it in the fridge to chill for 30 minutes.
Preheat the oven to 350 degrees F and line a cookie sheet (or two) with parchment paper.
Generously flour a surface and roll out the dough to ¼-inch thick. Using a 2-inch wide Linzer cookie cutter, punch out the main cookie shape from the dough and place it onto a cookie sheet with parchment paper. As needed, knead and re-roll dough until you have used up as much cookie dough as possible. You want there to be an even number of cookies (you should get about 40 from this recipe.)
Using the smaller Linzer cookie cutters, create the center shape by punching out the middle in half of the cookies. (You can place these pieces around the cookies and bake them too for snacks.)
Bake for 11-12 minutes, until the edges should just start to get golden. Remove from the oven and allow the cookies to cool on the pan for about 5 minutes. Then transfer to a wire rack to cool completely (about 30 minutes).
To assemble: Sift powdered sugar over the cookies with a cutout in the center - these are the "tops". Then take the "bottom" cookie (without a cutout) and spread about 1 teaspoon of jam almost to the edges. Place the top cookie over the jam and repeat until all the sandwich cookies have been assembled.
Notes
If you want to make the cookie dough in advance, you can. Once you reach the chilling step, leave the dough in the fridge until you're ready to use it. The cookie dough will need to sit out on the counter for about 2 hours to be soft enough to roll (if the dough is chilled for 1 or more hours).
To prevent smudging the powdered sugar, pick up the "top" cookies by the edge when placing them over the jam.
You can use any flavor of jam or jelly you like to fill these cookies.