Grind the oatmeal in a food processor or coffee grinder until finely ground. This will make it easier to incorporate into the dough.
In a large mixing bowl, sift the flour, add the ground oatmeal, baking powder, powdered sugar, and vanilla sugar. Whisk together the dry ingredients.
Cut the cold butter into smaller pieces. Add it to the flour mixture and quickly work it in with your fingertips or a pastry blender until it resembles coarse crumbs.
Grate the lemon zest into the mixture, then squeeze in the lemon juice. Add the egg and quickly knead the mixture into a smooth dough.
Wrap the dough in plastic wrap and refrigerate for at least 30 minutes to make it easier to roll out.
On a lightly floured surface, roll out the dough to about 3 mm (⅛ inch) thick. Use a cookie cutter or linzer cutter to cut out circles. Cut out the center of every other circle with a smaller cutter to create the signature linzer look, where the jam will be visible.
Place the linzer cookies on a baking sheet lined with parchment paper and bake in a preheated oven at 350°F (180°C) for 8-10 minutes, or until lightly golden brown.
Let the linzer cookies cool completely. Spread jam on the whole cookies and top with the cookies that have the centers cut out.
Dust with powdered sugar before serving.
To provide the best experiences, we and our partners use technologies like cookies to store and/or access device information. Consenting to these technologies will allow us and our partners to process personal data such as browsing behavior or unique IDs on this site and show (non-) personalized ads. Not consenting or withdrawing consent, may adversely affect certain features and functions.
Click below to consent to the above or make granular choices. Your choices will be applied to this site only. You can change your settings at any time, including withdrawing your consent, by using the toggles on the Cookie Policy, or by clicking on the manage consent button at the bottom of the screen.