In a large bowl with electric mixer at medium speed, beat butter, brown sugar,
and vanilla extract until fluffy. On low speed, gradually beat in 1 cup of the flour
until well mixed.
With a wooden spoon, mix oats and remaining flour until mixed and a soft dough
Divide dough into thirds. Place two dough pieces on one large cookie sheet
and the other piece on a small cookie sheet. Pat each to about a 5 1/2-inch circle.
Pierce each dough circle with the tines of a fork to form 8 equal wedges. Press
back of fork around edge of dough circles to decorate.