In a large bowl, beat the butter until smooth, add both sugars, beat until fluffy. Beat in the egg and vanilla, then add the flour, salt, cinnamon, and oatmeal. Cover the bowl and chill in the refrigerator until it is firm.

Preheat the oven to 160 C. Shape the dough into large marble sized balls and place on ungreased cookie sheets. Flatten each ball with the bottom of a drinking glass dipped into granulated sugar.

Bake the cookies for 12-15 minutes or until the cookies are just set and light golden brown. Cool the cookies on the cookie sheets for about a minute, then remove to wire racks to cool.