How to substitute unsweetened baker's chocolate for powdered cocoa in cake recipe My friend would like to make a chocolate cake using this recipe: 
HERSHEY'S "PERFECTLY CHOCOLATE" Chocolate Cake.

The ingredients:

2 cups sugar

1-3/4 cups all-purpose flour

3/4 cup HERSHEY'S Cocoa

1-1/2 teaspoons baking powder

1-1/2 teaspoons baking soda

1 teaspoon salt

2 eggs

1 cup milk

1/2 cup vegetable oil

2 teaspoons vanilla extract

1 cup boiling water

The directions:


Heat oven to 350°F. Grease and flour two 9-inch round baking pans.
Stir together sugar, flour, cocoa, baking powder, baking soda and salt in large bowl. Add eggs, milk, oil and vanilla; beat on medium speed of mixer 2 minutes. Stir in boiling water (batter will be thin). Pour batter into prepared pans.
Bake 30 to 35 minutes or until wooden pick inserted in center comes out clean. Cool 10 minutes; remove from pans to wire racks. Cool completely.
Frost with "PERFECTLY CHOCOLATE" CHOCOLATE FROSTING. Makes 12
servings.


They'd like to use baker's chocolate squares in place of the powdered cocoa.

Is this possible?
It's just a really basic (plain-vanilla, if you will ;) chocolate cake recipe. You'd be better off just finding a basic chocolate cake recipe that calls for unsweetened chocolate in the first place, especially if you're new-ish to chocolate cake.

Otherwise the substitution that Sobachatina suggests above requires some fancy recipe-adjusting work on your part. Cocoa &amp; fat (melted butter, usually) can be substituted for whole chocolate, but it's not really such an exact science, so I don't think the reverse substitution will give you the results you're looking for.