BRING porcini mushrooms and water to boil in medium saucepan; simmer on low heat 5 min. or until mushrooms are tender. Use slotted spoon to transfer mushrooms to cutting board. Add chicken broth to mushroom liquid in pan; bring just to boil. Reduce heat to low; cover to keep warm. Chop porcini mushrooms.
MELT butter in deep large skillet on medium heat. Add shallots; cook and stir 2 min. Add button and portobello mushrooms; cook and stir 2 min. Stir in porcini mushrooms; cook and stir 2 min. Add rice; cook and stir 1 min.
ADD warm broth mixture 1/2 cup at a time, stirring after each addition until most of the liquid is absorbed. (This will take about 20 min.) Stir in 1/4 cup cheese; top with remaining cheese and thyme.