1. Prep: Preheat oven to 325°F (160°C). Line a baking sheet with parchment paper.
2. Cream butter & sugar: Beat softened butter and powdered sugar until smooth and fluffy (~2–3 min). Add vanilla or zest if using.
3. Add flour: Gradually mix in flour and salt until a soft dough forms (don’t overmix).
4. Shape:
   • Slice-and-bake: Roll into a log, wrap in parchment, chill 30 min, then slice into ½” rounds.
   • Press-in pan: Press into an 8×8″ pan; score into squares before baking.
   • Cut-outs: Roll to ¼” thickness; cut with cookie cutters.
5. Bake 18–22 minutes, until edges are just golden (centers should stay pale).
6. Cool completely on pan, then dust with powdered sugar if desired.

💡 Pro Tips:
– Use cold butter for extra crumbly texture—or room temp for softer shortbread.
– Prick dough with a fork before baking to prevent puffing.
– Store in an airtight container for up to 2 weeks—they get better with time!

Prep Time & Nutrition (per cookie, makes 24):