Steamed Lamb Dumplings with Yogurt-Garlic Sauce Recipe

For the sauce, combine all the sauce ingredients and mix well. Store, covered and refrigerated, overnight. Sauté the onion and garlic in the oil until the onion is translucent. Combine all the remaining filling ingredients and mix well. (The filling can be made one day in advance.) Combine the flour and salt in the workbowl of a food processor. With the motor running, add the egg yolks and the oil in a steady stream. Slowly add enough water until the dough forms into a ball. Place the dough on a floured work surface and knead for 2 minutes. Cover the dough and allow to rest 30 minutes. (The dough can be made 1 day in advance.) Divide the dough in two, keeping 1 half covered while working with the other. Roll 1 half of the dough out very thin on a floured surface. Cut the dough into 3-inch [8-cm] circles. Repeat with the second half of the dough, keeping the cut circles covered as they are formed. To fill and form the dumplings, have a small dish of water handy. Place approximately ½ tablespoon [8 mL] of filling in the center of each dough circle and top with a piece of chilled butter. Gather the edges of the dough around the filling, moisten the inside edge, pinch, and twist to seal the top. Place the formed dumplings on parchment paper, without letting them touch, and cover with plastic film until ready to steam. (The dumplings may be made several hours in advance.) Place the dumplings into racks of a Chinese steamer that has been lined with oiled, perforated parchment paper, arranging them so that they do not touch. Heat several inches of water in the bottom of the steamer until simmering. Place the racks over the simmering water and cover to steam. If multiple racks are used, switch the top and bottom racks after 10 minutes to allow the dumplings to cook evenly. Cook for 10 minutes more. Serve the dumplings hot, 5 dumplings per serving, accompanied with the chilled yogurt-garlic sauce. Garnish with sprigs of cilantro and mint.