Heat oven to 350°F (175°C). Line baking sheets with parchment.
Beat butter, brown sugar, and sugar until fluffy.
Mix in eggs one at a time, then add vanilla.
Whisk flour, baking soda, salt, and cinnamon.
Stir dry mixture into butter mixture until just combined.
Fold in oats, cranberries, and nuts if desired.
Scoop tablespoons of dough 2 inches apart. Bake 10–12 minutes until edges are golden.
Cool 5 minutes on the sheet, then move to racks.