1In 2-quart saucepan, mix sugar and cornstarch. Stir in whipping cream with whisk. Heat to boiling over medium heat, stirring constantly; boil 1 minute or until thickened. Remove from heat. Stir in butter until melted. Stir in coconut, sour cream and vanilla. Place plastic wrap directly on surface of custard; refrigerate at least 3 hours.
2Heat oven to 350°F. Place paper baking cup in each of 24 regular-size muffin cups. In large bowl, beat cake mix, coconut milk, water and eggs with electric mixer on low speed 30 seconds. Beat on medium speed 2 minutes. Stir in finely chopped pecans. Divide batter evenly among muffin cups.
3Bake 18 to 20 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes; remove from pans to cooling racks. Cool completely, about 30 minutes.
4Spread coconut custard over cupcakes; sprinkle with coarsely chopped pecans. Store in refrigerator.