Grease and flour a 10-inch cake pan with 3-4 inch high sides. Set aside. Sift together flour, soda and salt. Set aside. In a large mixing bowl cream butter, cocoa and sugar for approx. 3 minutes. Add eggs and vanilla and beat until smooth and creamy. Add sour cream and mix until smooth. Add flour mixture and mix just until blended. Slowly add boiling water and beat until smooth. Bake in a preheated 350 degree oven for 40-45minutes or until cake springs back when lightly touched. Cool in pans for 10 minutes. Invert to a cooling rack to cool. Bake cupcakes for 18-20 minutes.

1. Remove the eggs from the refrigerator so they will be room temperature when ready to use.

2. In a small heavy saucepan, combine the sugar, cream of tartar, and salt. Stir the mixture to combine evenly; add the water.

3. Over medium heat, bring the mixture to a boil, stir continuously until it is clear. Allow the mixture to boil until it reaches the soft ball stage or 240°F on a candy thermometer.

4. Remove from the heat and allow it to set while beating the egg whites.

5. Beat the egg whites and vanilla in a large, wide bowl until they form soft peaks. Be sure to use a wide bowl so that you have enough room to beat the frosting while you are adding in the sugar mixture without pouring it into the beaters.

6. Once the eggs are at a soft peak, begin to slowly pour the boiled sugar mixture into the egg whites Pour the mixture along the side of the bowl while beating the two together.

7. Make sure to pour the sugar mixture in a slow steady stream off to one side and continue to beat the frosting the entire time. Do not pour the sugar mixture into the beaters. To incorporate it into the egg whites, move the beaters back and forth into the area where the sugar syrup has been added.

8. Once all of the sugar syrup has been added, beat for 7 minutes until the frosting is thick enough to form stiff peaks.