Step 1

Dry Ingredients: Add the flour, almond flour, cornstarch, and salt to a medium bowl and whisk until combined; set aside.

Step 2

Wet Ingredients: Add the sugar and lemon or orange zest to a large bowl or stand mixer. Use your hands to massage the zest into the sugar until it is evenly distributed (this creates a stronger citrus flavor!). Add the butter and beat (using a handheld or stand mixer) over low speed until the butter is light and fluffy, 3 to 5 minutes. Scrape the sides of the bowl with a spatula as necessary. Add the milk, vanilla, and almond extracts and beat for 1 more minute.

Step 3

Combine: Add the dry ingredients to the bowl and mix until the mixture is crumbly, but will pinch together. Try not to overmix.

Step 4

First Chill: Divide the dough in half (I like to use my food scale for the most accurate results). Place each half on a sheet of plastic wrap; flatten into a disc and fully wrap. Refrigerate the dough for at least 1 hour, up to overnight.

Step 5

Shape the Cookies: Line two baking sheets with parchment paper and set aside. Lightly flour a cutting board and rolling pin. Remove one disc of dough from the fridge, unwrap, and knead it on the cutting board for 30 seconds - 1 minute until it is pliable. Sprinkle the top of the dough with more flour and roll it out until it is about 1/4" thick. Use a round 2 1/2” cookie cutter to cut out your cookies, then use a smaller cookie cutter to cut out the center “window” of each cookie. Use a bench scraper or spatula to transfer each cookie to the baking sheet, leaving at least 1/2" of space between each cookie. Repeat with the remaining dough, dusting with more flour if necessary. Each disc of dough should make about 15 cookies.

Step 6

Second Chill: Transfer the cookie sheet back to the refrigerator and chill for an additional 30 minutes. In the meantime, preheat the oven to 350F and repeat step 5 with the second disc of dough; this time, do not cut out the center window for each cookie (these will be the bottoms). Refrigerate the cut cookies for at least 30 minutes before baking.

Step 7

Bake: Bake each baking sheet of cookies in the middle rack of the oven for 8 to 10 minutes, only until the bottoms of the cookies are slightly golden. Baking the cookies for less time will result in chewy cookies, while longer will make a more crunchy shortbread.

Step 8

Cool: Remove the cookies from the oven and let sit on the baking tray for at 5 minutes to set, then transfer to a wire rack and let cool completely. Cool the cookie “tops” (center holes) and “bottoms” (solid circles) on separate wire racks, if possible.

Step 9

Assemble: Place the powdered sugar in a sifter or fine metal sieve and dust it generously over the cookie tops. Assemble each Linzer cookie by spreading 1/2-1 teaspoon of jam over each cookie bottom, then sealing it with the powdered cookie top. Repeat with the remaining cookies.

Step 10

Serve & Store: Store any leftover cookies in an airtight container at room temperature for up to 5 days. If you are concerned about your jam spoiling you can also store them in the refrigerator, but they will be more chewy.