In a large bowl, cream together the butter and sugar until light and fluffy. Stir in the beaten egg and extract. Add the flour, ground almonds and lemon zest and mix until the dough comes together.
Turn the dough out onto a floured surface and knead into a ball. Divide the dough in half and then roll each half into a log, about 1 1/2 inches in diameter. Wrap each log in plastic wrap and refrigerate for 1 hour (the dough can be frozen at this point for a later use).
Preheat the oven to 350 degrees F. Line 2 baking sheets with parchment paper.
Remove the dough from the plastic wrap and slice into 1/4-inch-thick rounds. Place the cookies onto the prepared baking sheets and bake until golden brown at the edges, about 15 minutes. Let cool on the baking sheets for 3 or 4 minutes before transferring to wire cooling racks to cool completely, or just eat warm from the oven.