Place porcini mushrooms in 2-cup measuring cup; add enough hot water to measure 2 cups. Let stand until mushrooms are soft, about 20 minutes. Drain mushrooms, reserving soaking liquid. Coarsely chop porcini mushrooms. Cook tortellini in large pot of boiling salted water until just tender but still firm to bite, stirring occasionally. Meanwhile, melt butter in large skillet over medium-high heat. Add shallots; sautee until golden and tender, about 4 minutes. Add mushrooms and 3 teaspoons thyme; saute 2 minutes. Stir in 1 cup mushroom soaking liquid and cream; boil until thickened to light sauce consistency, about 3 minutes. Season to taste with salt and pepper. Drain tortellini; return to same pot. Add mushroom mixture and toss to coat. Stir in 1/2 cup cheese. Season with salt and pepper. Transfer tortellini to bowl; sprinkle with 1/4 cup cheese and 1 teaspoon thyme.