Lemon Cookie Sandwiches

These lemon cookie sandwiches start as a simple icebox dough: butter, sugar, yolks and a splash of vanilla shaped into a tight log and chilled until firm enough to slice into thin, even rounds. The chill is what gives the baked cookie its delicate snap, so do not shortcut the four-hour rest.

Half the slices get a brushing of beaten egg white and a scatter of finely chopped nuts before baking, which is the trick that gives the tops their toasty, glittery crown. Once cooled, every plain cookie gets a swipe of bright lemon filling whisked from powdered sugar, soft butter, fresh juice and zest.

Sandwiched together, you get a buttery shortbread bite with a tangy lemon middle and a crunchy top, the kind of cookie that disappears off a holiday tray in under an hour.

Pro Tips

• Slice the chilled log with a thin, sharp knife and rotate a quarter turn between cuts to keep the rounds perfectly circular instead of oval.
• Watch the oven closely. At 400°F (200°C) these go from pale to over-browned in under a minute. Pull them when only the edges have color.
• Make the lemon filling with freshly squeezed juice and finely grated zest. Bottled juice tastes flat and dulls the whole cookie.
• Sandwich the cookies the day you serve them. Filled too early, the moisture softens the crisp shortbread.

Variations

• Swap lemon for Meyer lemon or pink grapefruit zest and juice for a softer, floral citrus.
• Press a tiny piece of crystallized ginger into the nut topping before baking for a warming bite that plays beautifully against the lemon.
• Use finely chopped pistachios in place of walnuts for a green-and-gold holiday look.