Step 1
Preheat oven to 350 degrees F (175 degrees C). Line two 9 inch pans with parchment paper. Cut 9 inch circles so bottoms will be smooth. Springform pans are preferred.
Step 2
Melt 2 squares chocolate in saucepan over low heat. Set aside.
Step 3
In a medium bowl sift together cake flour 1 1/2 cup sugar baking powder 1 teaspoon salt and soda.
Step 4
In a large bowl with electric mixer blend 1/2 cup shortening 1 1/4 cup evaporated milk and 1 teaspoon vanilla. Add flour mixture and beat with mixer 2 minutes at medium speed.
Step 5
Add 2 eggs and mix until eggs are just blended. Add the melted 2 squares of chocolate (drizzle in while blending). Beat 1 minute at medium speed. Divide batter into two 9 inch pans.
Step 6
Melt remaining 2 squares of unsweetened chocolate. Drizzle melted chocolate in ring shape onto batter about 1 to 2 inches from edge. Using a butter knife or thin spatula swirl chocolate into pinwheel pattern with a large circular motion. Don't swirl too much as you want chunks to remain. Press knife or spatula all the way to bottom of pan as you swirl.
Step 7
Bake at 350 degrees F (175 degrees C) for 30 to 35 minutes or until a toothpick inserted into center of cake comes out clean. Cool completely.
Step 8
To make the filling: Melt 1 square of chocolate. In a large bowl combine 2/3 cup shortening 1/3 cup sugar 1/4 cup evaporated milk 1/4 teaspoon salt 1 teaspoon vanilla and water. Add melted chocolate and beat on high speed for 10 minutes.
Step 9
Using a long serrated knife divide each cooled cake into 2 layers. Spread filling between layers. Use prettiest pinwheel layer as top layer.