Preheat the oven to 350 degrees F.
To make the cookies:
Combine butter, sugars, lemon zest
, and vanilla in the bowl of a stand mixer
with the paddle attachment. Mix on medium speed until all ingredients come together and are light and fluffy. Add the egg. Sift
together the flour, baking soda, nutmeg
, and salt, and add to the butter mixture in three parts, waiting until each is well mixed before adding the next. Add the oats last, mixing just until combined. Chill the dough in the freezer for 5 minutes.
Transfer the dough to a large surface covered with a layer of parchment paper. Top with another layer of parchment and gently roll the dough into a 1/4-inch-thick sheet. To prevent the cookies from sticking as you cut them, carefully remove the top layer of parchment and drizzle
some flour over the sheet of dough. Replace the parchment, flip the dough, and release the parchment on the other side. Cut the dough
into 2 1/2-inch round cookies and space about 1/2 inch apart on an ungreased cookie sheet. Gather any leftover scraps of dough and roll and cut as described above. Repeat until you have no dough left. Bake the cookies for 15 to 20 minutes, turning the pan 90 degrees halfway through baking, until golden brown in color but still soft in the center. Transfer the cookies to a cooling rack
. Let cool completely before filling.