In a medium bowl, whisk together the flour, cinnamon, corn starch, and baking soda; set aside.
Combine the butter with both sugars; beat on medium speed until light and fluffy.
Reduce speed to low; add the salt, vanilla, and eggs. Beat until well mixed, about 1 minute.
Add flour mixture; mix until almost combined.
Stir in the oats, cover and chill dough for one hour to overnight.
Preheat oven to 375 degrees.
Use a small ice cream scooper (two tablespoons) to Drop heaping tablespoon-size balls of dough about 2 inches apart on baking sheets lined with parchment paper.
Bake until cookies are golden around the edges, but still soft in the center, 8 to 10 minutes.
Remove from oven, and let cool on baking sheet 1 to 2 minutes. Transfer to a wire rack, and let cool completely.