Instructions

1. Cut the butter into cubes and let it soften at room temperature for 10 minutes.
   
2. Place the softened butter in a large bowl. Add the sugar and egg, and beat with a mixer for 2-3 minutes.
   
3. Add the flour, salt, and lemon zest (if using). Mix with a spoon, then knead with your hands until the dough is smooth and homogeneous.
   
4. Form the dough into a ball, wrap it in plastic wrap, and refrigerate for at least 30 minutes before using.