Step 1: Make the Cookie Dough

1. In a large bowl, cream butter and sugar together until light and fluffy (about 2 minutes).
2. Add egg yolk and vanilla extract, mixing until combined.
3. In a separate bowl, whisk together flour, cinnamon, and salt.
4. Gradually add the dry ingredients to the butter mixture and mix until a dough forms.
5. Divide dough in half, shape into discs, wrap in plastic, and chill for 30 minutes.

Step 2: Roll and Cut the Cookies

1. Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.
2. Roll out dough on a lightly floured surface to ⅛-inch thickness.
3. Use a heart-shaped cookie cutter to cut out cookies.
4. For half of the cookies, cut a smaller heart shape in the center to create “windows.”
5. Transfer cookies to baking sheets and chill for 10 minutes (helps keep their shape).

Step 3: Bake the Cookies

1. Bake for 10-12 minutes, or until edges are lightly golden.
2. Let cool on the baking sheet for 5 minutes, then transfer to a wire rack.

Step 4: Assemble the Linzer Cookies

1. Mix strawberry jam and lemon juice, then spread ½ teaspoon of jam onto the whole cookies.
2. Dust the top heart cutout cookies with powdered sugar before placing them over the jam layer.
3. Gently press together and let set for 30 minutes before serving.