In small saucepan, combine mango nectar and crushed peppercorns. Bring to boil, then reduce heat and simmer 15 to 18 minutes or until reduced to 1/3 cup. Let cool 10 minutes and strain through a fine wire-mesh strainer, discarding solids.
In small saucepan, whisk together reduced mango nectar, sugar, egg yolks and lemon juice. Cook over medium-low heat 5 to 8 minutes or until mixture thickens enough to coat the back of a spoon, stirring constantly. Remove from heat and stir in butter, 1 piece at a time, until melted. Cover with plastic wrap and refrigerate until cold.
In large bowl, combine flour, cocoa powder, baking powder, baking soda and salt.
In large bowl, beat butter, sugar and 1/4 teaspoon peppercorns with electric mixer until light and fluffy. Add egg and vanilla extract; beat until well combined. Alternately add flour mixture and buttermilk in three additions, beating until just combined. Spoon 1 tablespoon batter into each pan cavity.
Bake 9-11 minutes or until toothpick inserted in center of cakes comes out clean. Cool in pan 10 minutes. Cool completely on cooling grid.
Fill centers of cakes with about 1 teaspoon curd and sprinkle with remaining peppercorn.