Bring water and broth to a boil in a saucepan. Add porcini; remove from heat, and let stand 15 minutes. Drain in a colander over a bowl, reserving liquid. Chop porcini; set aside.
Combine flour, salt, garlic, and beef, tossing well to coat. Heat 1 teaspoon oil in a large Dutch oven over medium-high heat. Add half of beef mixture; sauté 4 minutes or until browned. Remove from pan. Repeat procedure with 1 teaspoon oil and remaining beef mixture. Wipe pan clean with a paper towel; coat with cooking spray. Add button and cremini mushrooms; cover, reduce heat to medium, and cook 10 minutes or until mushrooms release liquid. Stir in the reserved porcini liquid, chopped porcini, beef mixture, and tomato paste; bring to a boil. Cover, reduce heat, and simmer 45 minutes.
Preheat oven to 450°.
Combine remaining 1 teaspoon oil and onion on a foil-lined jelly-roll pan; toss well to coat. Bake at 450° for 25 minutes, stirring twice.
Add roasted onion, rosemary, and pepper to stew. Cover and simmer stew an additional 30 minutes or until beef is tender. Sprinkle with parsley.
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