For the dough combine flour, ground chipotle, sugar and salt in a food processor and pulse until combined. Add butter and continue pulsing until it resembles coarse crumbles. Transfer ingredients into a large mixing bowl and slowly add ice water about one quarter cup at a time, stirring between each addition until a rough ball forms. Use less or more water as needed. Turn out dough onto a large working surface and divide dough in half. Form each into a disk, wrap in plastic wrap and refrigerate at least 2 hours.
For the filling cover sweet potatoes with water in a large pot and bring to a boil. Cover, reduce heat to a low boil and cook until fork tender about 20 minutes. Drain and transfer to a medium mixing bowl. Using a mixer or back of a fork mash sweet potatoes into a puree then stir in black beans and corn until evenly distributed. Cover and refrigerate until completely cooled.
To assemble empanadas work with one disk at a time on a lightly floured surface and roll out into a circle about 1/8-inch thick. Using a 3-inch circular cookie cutter press out as many circles as possible from the dough this should be about twenty circles. Repeat process with second batch of dough and arrange circles on two baking sheet lined with parchment paper or foil. If dough has become difficult to work with you may want to chill again before filling them.
Place one rounded teaspoon of filling into the center of each circle, using your finger wet the edges with water and fold circles in half until the edges meet. Press edges together to seal then use a fork to crimp, dipping the fork into flour if it is sticking. Continue until all circles are filled and formed.
To bake preheat oven to 425 degrees F. Brush empanadas with egg wash and cook about 20 minutes or until golden brown. Allow to cool about five minutes before serving or store in refrigerator for up to three days. You can also freeze them and to cook bake at 425 degrees for about 25 minutes.
For the dip in a medium mixing bowl combine sour cream, lime zest and juice and cilantro and mix well. Serve dip with empanadas.