Preheat oven to 475°.
Place squash on a nonstick jelly-roll pan coated with cooking spray. Bake at 475° for 20 minutes or until tender, turning after 10 minutes.
Reduce oven temperature to 325°.
Combine broth, water, wine, and tarragon in a saucepan; bring to a simmer. Keep warm over low heat.
Cook pancetta in a large ovenproof Dutch oven over medium-high heat until crisp. Remove pancetta from pan; drain on a paper towel. Discard pan drippings. Add onion and oil to pan; sauté 10 minutes or until onion is tender. Add garlic; sauté 1 minute. Add rice to pan; sauté 1 minute. Stir in broth mixture; bring to a boil over medium heat. Reduce heat, and simmer over low heat, uncovered, for 10 minutes. (Do not stir; rice will have a liquid consistency similar to stew.)
Place pan in oven; bake at 325° for 15 minutes. Remove from oven. Stir in the squash, pancetta, cheese, salt, and pepper. Cover with a clean cloth; let stand 10 minutes (rice will continue to cook). Sprinkle with pine nuts. Garnish with tarragon sprigs, if desired.
Perfect wine: Clos du Val Chardonnay 2001 (Carneros, CA), $21. This chardonnay has refined flavors reminiscent of custard, caramel, apple tarts, and honey. There's a hint of oak, but the wine is not superbuttery, oaky, or toasty. This wine is complemented by the savoriness of the rice and the sweetness of the squash.