Beat the butter and sugar together until light and fluffy. You can use a stand mixer with paddle attachment, or just do this by hand with a wooden spoon.
Add the egg, egg yolk, vanilla, and almond extract and beat until combined.
Pass the almond flour through a fine mesh sieve into the bowl and mix it in to form a thick paste.
Sift in the flour, cinnamon, and salt and mix just until it combines into a soft dough - be careful not to overmix.
Tip the dough out onto a lightly floured work surface and knead it gently until a smooth ball forms. Flatten the dough into a disk shape, wrap with plastic wrap and chill for at least 30 minutes, or up to 2 days.
Unwrap the dough and roll it out until it is about ⅛ inch thick. If it's too hard to work with, let it sit on the counter to warm up for a few minutes first.
Use a round cookie cutter (with or without fluted edges) to cut out rounds. I used a 2-inch cookie cutter, which made about 36 cookies - but you can use any size (or shape) you like.
Transfer the cookie rounds to two baking sheets lined with parchment paper. Cut a heart shape out of the middle of half of the cookies. Tip: Keep the 'tops' and 'bottoms' on two different cookie sheets as they bake faster with the middle cut out.
Put the cut out cookies in the fridge to chill for 30 minutes before baking - this will help them to hold their shape. Meanwhile, preheat the oven to 350°F / 180°C (160° fan-assisted).
Bake until lightly golden brown, this will take roughly 12 minutes for the bottoms and 9 minutes for the tops. Remove from the oven and let the cookies sit on the tray for 5-10 minutes before transferring to a wire rack to cool.
Once cooled, dust the top cookies (the ones with the hearts cut out) generously with powdered sugar - it's better to do this before assembling so you don't get any powdered sugar on the jam heart windows.
Spoon about a teaspoon of jam onto each of the bottom cookies and spread it out evenly. Don't overfill them or the jam may ooze out of the sides.
Place the top cookies on top of the bottom cookies and press down gently.
Notes
Ingredients Notes:Classic Linzer Cookies are filled with raspberry jam, but you can fill these with anything you like. It's best to use seedless jam, or you can make homemade berry puree for an extra-special filling. Make sure your butter and eggs are at room temperature before beginning. I always recommend measuring your ingredients with a kitchen scale as it's far more accurate and will give better results.