Grease a large (10 x 15) baking pan (NOTE: smaller pans mean a taller bake, and longer baking time).
Cream the butter and sugar, then blend in the pumpkin.
Blend in the eggs.
In a separate bowl, mix flour, salt, baking powder, baking soda, cinnamon, and nutmeg.
Blend dry mixture into the pumpkin mixture.
Add nuts (optional).
Spread into greased baking pan, and cook for 30 minutes, or until tooth pick comes out clean and dry.
Allow to cool completely before adding frosting. You can spread a coating of cream cheese frosting over the entire thing and then cut 1x2" rectangles or 2x2" squares, or you can cut the pieces first and then pipe the frosting onto each piece.