With electric mixer on medium speed, beat cream cheese, 1/2 cup sugar, and 1/4 teaspoon salt in medium bowl until smooth, about 30 seconds. Beat in egg whites and 2 tablespoons sour cream until combined, about 1 minute. Stir in chocolate chips and set aside.
Whisk remaining sugar, remaining salt, flour, cocoa, and baking soda in large bowl. Make well in center, add remaining sour cream, water, butter, and vanilla and whisk until just combined. Divide batter evenly among 24 cupcake liners and top each batter with 1 rounded tablespoon cream cheese mixture. Bake until tops of cupcakes just begin to crack, 23 to 25 minutes. Cool cupcakes in tins for 10 minutes before transferring to wire rack to cool completely. (Cupcakes can be refrigerated in airtight container for up to 2 days.)
Time to Prepare: about a half hour
Submitted By: Betsy
Original Source: Cooks Illustrated
These cupcakes are not overly sweet since they lack frosting. I think they are better the next day, right out of the fridge (with morning coffee actually.)