Make the dough. First, grind the almonds finely (if not using almond flour) and set aside.
In the bowl of a stand mixer or with a hand mixer, beat the butter and sugar together on medium speed until light and fluffy, 2 to 3 minutes.
Add the egg yolk, vanilla and lemon zest (if using) and beat again to combine. Add the flour, ground almonds and salt (if using). Beat on low speed until just combined. Do not over-mix the dough at this stage. It will feel soft and sticky. See photos below.
Scrape the dough out onto a large piece of clingfilm and flatten into a disc about an inch thick. Refrigerate for at least 1 hour. I like to make the dough on day one to space out the prep-time a little bit. So if you're refrigerating the dough longer than 1 hour, leave it out at room temperature for about 20 mins until it has softened enough that you can roll it, but it isn't warm.
Cut the chilled dough in half and keep one half wrapped and in the fridge. Place the other half on a silicone baking mat. I find this much easier than rolling the dough out on the kitchen counter or between sheets of paper as they tend to slide around. It helps if you have more than one baking mat to speed up the process.
Cover the dough with a sheet of non-stick baking paper and roll into a roughly 10 inch circle, 1/4-inch thickness. Don't make the dough so thin that the cookies burn or so thick that they remain raw.
Cut out your shapes, leaving about 1/2 inch gap between each. (These are the bottom cookies. I used tree, star and gingerbread man cutters that were about 2 to 3 inches in length. Use any you like, even a simple round cutter).
By this time the dough would have warmed up a little so slide the mat onto a baking tray and place it in the freezer for 15 minutes. Then, use a metal spatula or knife to easily lift and cut away the scraps, leaving the shaped cookies on the mat. This way you don't need to transfer the cookies to another tray and risk them breaking or losing their shape. The cookies should always be cold before going in the oven.
While the dough is in the freezer, preheat the oven to 165 C. I found the original temp of 175 C a bit too high, but feel free to adjust this because it depends on the size and thickness of your cookies.
Bake the cold cookies for 5 to 8 minutes, until the edges have lightly browned but the surface is still soft and a little pale. Let them cool on the tray for 5 minutes to firm up, then transfer to a wire rack to cool completely. You'll have some cookies that do become too brown, that's ok, this dough makes enough that a few imperfect ones can be snacked on as is!
Gather the dough scraps and repeat the roll-cut-free-bake process with the remainder of the dough. If you're making a variety of shapes, make a note of how many of each you're cutting out so you can have the same number from the other half the dough (which will be the top cookies).
When all your top cookies are done, roll and cut out the second half the dough in the same way. The difference here is you will cut out a small shape in the center of each cookie so the jam can peek through. Use a small round piping tip or other instrument for this cut-out, or if you have mini versions of the same cookie cutter, you can use that too.
Freeze each batch just as you did with the top cookies, then peel away the scraps and gently take out the center cut-outs as well so the cookies have the hole in the center.
Bake these also for 5 to 8 minutes, until lightly browned on the edges. Let them cool on the tray for 5 minutes to firm up, then transfer to a wire rack to cool completely.
Gather the dough scraps and repeat the roll-cut-free-bake process with the remainder of the dough to make all your bottom cookies.
Once you have all your cookies baked and cooled, you can store them in an airtight tin and assemble them the next day, if not immediately.
To assemble, first make pairs of the cookies so you can match the neatest ones (some might break or be too brown or uneven). You should have between 15 to 18 cookie sandwiches.
Next, spread a teaspoon of jam on each of the bottom cookies, in a thin, even layer.
Place the top cookies on a wire rack with a tray underneath. Dust half of the top cookies with icing sugar using a small sieve. For the other half, make the lemon glaze by mixing the icing sugar and lemon juice until it's of a drizzle-able consistency (add more juice if you need to as long as the glaze isn't too sour). Use a small spoon to drizzle the glaze over the remaining top cookies. This glaze hardens as it sets. You can of course make more glaze if you want to decorate all the cookies the same way.
Now cover the bottom cookies (the ones with jam) with the decorated top cookies and very gently press down to help them stick. Let them rest for about 30 minutes at room temperature before you dig in. They actually taste even better the next day and will soften slightly as well so I recommend sampling a couple and then leaving the rest till later!
Store in an airtight box at room temperature for 2 to 3 days, in the fridge for about a week and in the freezer for longer. I found that after refrigeration or freezing, the texture improved further and the cookies were more sandwich-y, even while cold. I hope you enjoy these! Merry Christmas!