Heat oven to 300° convection.
Butter baking pan. A 7x11” pan makes a thinner cookie; an 8x8” pan, a thicker cookie.
Combine 2½ tablespoons sugar with 1 teaspoon cinnamon. Dump mixture into the buttered baking dish and shake pan so the inside is completely coated. Pour the extra cinnamon-sugar mixture into a small bowl and reserve.
Add the flour, sugar, salt and cinnamon to the bowl of a food processor. Pulse a couple of times to combine.
Cut the butter into pieces and add to the dry ingredients, along with the vanilla extract. Process until a crumbly dough is formed. Don’t overmix but be sure there are no pockets of dry flour. It helps to stop the processor once to “stir” the contents together. The dough is ready if it holds together when you squeeze it.
Dump the dough into the prepared pan. Use the palms of your hands or the bottom of a measuring cup to press down the mixture until it is totally smooth. Dip the measuring cup in sugar to keep the cup from sticking to the cookie dough.
Sprinkle the remaining cinnamon-sugar mixture evenly on top. Use a fork to prick the dough all over.
Bake for 40-45 minutes or until the top is deeply golden brown and dry to the touch. As soon as it comes out of the oven, cut into squares (cut these any size you want). I cut the 7x11” pan into 4x6 or 24 pieces. Cool before removing from pan.