Beat butter and sugar for 5–6 minutes until fluffy.
Mix in eggs one at a time.
Add lemon extract, vanilla, and optional zest.
Add flour and 7 Up in alternating stages.
Grease and flour the bundt pan.
Bake at 325°F for 1 hour 10 minutes.
Rest 1 minute, then turn onto rack.
Mix powdered sugar, milk, and lemon flavor; drizzle on cooled cake.
