Preheat the oven to 350° F and line a baking sheet with parchment paper.
In a medium saucepan over low heat, combine the butter, sugar and corn syrup. Stir often until the butter is melted and the sugar dissolves. Increase the heat to medium-high, stir constantly and bring to a boil. Once the contents begin to boil, remove from the heat. Stir in the flour and salt until well incorporated. Finally, stir in the ground almonds, lemon zest and vanilla extract.
Using a teaspoon, drop the batter onto the baking sheet. Bake the cookies until evenly light brown, about 10 minutes. At the 5-minute mark, turn the baking sheet around in the oven to ensure even baking. The cookies won’t begin to spread till about 6 minutes into baking.
Cover a cooling rack with paper towels. When the cookies are done baking, place them on the paper-toweled covered wire rack and let cool.