Roast Lamb with Mint Sauce

1 bunch fresh mint
1/2 C sugar
1/2 C + 4 tsp. water
1 C rice vinegar
1 T potato starch
1 red onion sliced
olive oil
4 garlic cloves, peeled
6 sprigs fresh parsley
6 sprigs fresh rosemary
6 sprigs fresh thyme
1 7lb. boneless leg of lamb
salt and pepper
To make the sauce, remove the tough stems from the bunch of mint and coarsely chop the leaves. Set aside. Combine the sugar and the 1/2 C water in a medium saucepan, bring to a simmer over medium heat, stirring until the sugar is dissolved. Add the vinegar and the chopped mint, increase the heat and bring the mixture to a boil. Meanwhile mix the reaining 4 tsp. water and potato starch in a small bowl, whisk until smooth.  Add the dissolved starch to the mint mixture, beating with a whisk until blended. Boil until slightly thickened., about 1 minute. Remove the pan from the heat and allow to cool for 30 minutes.  Refrigerate covered, until chilled, 1-6 hours. To prepare the lamb: pour 2 T olive oil on the bottom of a crockpot. Place onion and lamb in the crockpot. Place fresh herbs, salt and pepper on top of the lamb. Cover and cook on low for 8 hours. Carve the roast and serve with the mint sauce.