Combine onion, carrot, 1 garlic clove and 1.5 tsp. olive oil in heavy medium saucepan. Cook over low heat until veggies are tender, stirring frequently, about 8 minutes. Add curry powder and saute 2 minutes. Add stock and rosemary and bring to a boil. Reduce heat to medium and cook until reduced to 2.5 cups, about 25 minutes. Strain through sieve set over bowl, pressing on solids. Heat remaining 1.5 tsp. olive il in heavy large nonstick skillet over medium-low heat. Add mushrooms and cook until almost no liquid remains in skillet, stirring frequently, about 10 minutes. Increase heat to medium-high. Add shallot and remaining minced garlic and saute 5 minutes. Add strained stock and boil until liquid is reduced to 2 cups, about 10 minutes. Transfer to blender and blend until smooth, about 2 minutes. Strain through a sieve, set over a saucepan. Mix in lemon juice. Season to taste with pepper. (Can be prepared one day ahead. Cover and refrigerate.) Bring sauce to a simmer, mix in tarragon and serve. Serve over grilled pork, veal or chicken.