Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch baking pan.
In a medium saucepan over medium heat, melt butter. Add water and bring to a boil.
In a large bowl, mix together flour, baking powder, salt, eggs, cocoa, sugar, and vanilla extract. Pour in boiling butter and water and mix until smooth.
Pour batter into prepared pan. Sprinkle with chopped walnuts, if desired. Bake in preheated oven for 30 minutes, or until a toothpick inserted into the center comes out clean.
Let cool before frosting.
Interesting Facts
This cake can be frozen for up to a month.
The name “Alaska” comes from the fact that it was originally served in Alaska in the 1950s.
It is sometimes referred to as a “Sheet Cake” because it is baked in a sheet pan.