Preheat oven to 350*F. Spray a 9″ x 13″ jelly roll baking pan (cookie sheet). Place a piece of parchment paper on the sprayed sheet, then spray one more time – set aside.
In a large mixing bowl sift together the flour, sugar, baking powder, cinnamon and salt.
Add butter, milk, and vanilla. With a hand mixer, beat for 2 minutes, occasionally scraping down the sides of the bowl.
Add eggs and beat for 2 minutes more.
Pour batter into baking pan.
Bake 25 minutes, or until a toothpick inserted into the center comes out clean. Remove from oven and cool completely. Cut the cake into three equal pieces. These will be the three layers to your rectangle cake.
Whipped Cinnamon Frosting
In a medium bowl, combine pudding mix with milk, cinnamon and vanilla. Mix until smooth. Gently fold in whipped topping until no streaks remain. Spread even layer on each layer prior to completely covering cake.