Preheat the oven to 350º Fahrenheit. Line a baking sheet with parchment paper (or a silpat).
Add butter to a small saucepan and melt over low heat. Allow the butter to cool for 2 minutes.
Combine the melted butter white and brown sugars. Use an electric mixer and beat ingredients on medium speed. Add one egg yolk + one whole egg, vanilla extract, lemon zest and juice. Continue to mix all ingredients.
Slowly add flour and continue to beat until you have a thick, smooth batter. Chill in the fridge for 15 minutes.
Place one tablespoon cookie batter and onto the baking sheet. Bake for 15 minutes. Remove from oven and let cool.