Heat oven to 375 F. Beat butters and sugar until fluffy. Beat in egg and vanilla. Add combined flour, baking soda and salt. Mix well. Stir in oats and chocolate chips.
Drop by rounded tablespoonfuls onto ungreased cookie sheet. Bake 8-9 minutes for a chewy cookie, 10-11 minutes for a crisp cookie. Cool 1 minute on cookie sheet, remove to wire rack, cool, store tightly covered.