Preheat the oven to 350 degrees F. Spray a 15x10x1 inch sheet pan with nonstick spray.
In a large bowl, use a whisk to combine the pumpkin, sugar, Stevia and oil. Whisk in the eggs.
In a separate bowl, whisk together the flour, baking soda, cinnamon and salt. Whisk the dry ingredients into the wet ingredients.
Scrape the batter into the prepared pan, and spread evenly. Bake for 25 to 30 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool completely.
FROSTING
Place the butterscotch chips in a glass microwave safe bowl. Melt in bursts, just until melted and stirring until smooth.
In a medium bowl, use a hand mixer to combine the cream cheese and butter until smooth. Add the sugar and Stevia and mix until combined. Add the melted chips, milk and vanilla and mix until smooth.
Spread the frosting evenly over the cake. Refrigerate until ready to serve.