How to Make It
Combine 2 cups boiling water and porcini mushrooms in a bowl; cover and let stand for 15 minutes or until the mushrooms are soft. Drain through a sieve over a bowl, reserving soaking liquid. Chop the porcini mushrooms.
Heat a large nonstick skillet over medium heat. Add 1 1/2 teaspoons olive oil to pan, and swirl to coat. Coarsely chop 1 pancetta slice. Add chopped pancetta to pan; cook for 3 minutes, stirring occasionally. Add 1 3/4 cups shallots, 2 teaspoons rosemary, 1/4 teaspoon salt, and 1/4 teaspoon pepper; cook for 7 minutes or until shallots are tender, stirring occasionally. Stir in reserved mushrooms. Cool slightly.
Slice 1 turkey breast half lengthwise, cutting to, but not through, other side. Open halves, laying turkey breast flat. Place plastic wrap over turkey breast; pound to 1/2-inch thickness using a meat mallet or small heavy skillet. Spread half of shallot mixture over turkey breast; roll up jelly-roll fashion, starting with long sides. Sprinkle with 3/8 teaspoon salt and 1/4 teaspoon pepper. Arrange 4 pancetta slices evenly on top of turkey roll. Secure at 2-inch intervals with twine. Repeat procedure with remaining turkey breast half, shallot mixture, 3/8 teaspoon salt, 1/4 teaspoon pepper, and 4 pancetta slices.
Preheat oven to 325°.
Heat a large Dutch oven over medium-high heat. Add remaining 1 1/2 teaspoons oil to pan; swirl to coat. Add turkey rolls to pan; cook 6 minutes or until browned, turning after 3 minutes. Add remaining 1/4 cup shallots, carrot, celery, and wine to pan. Bring to a boil; cook until liquid is reduced by half (about 2 minutes). Stir in reserved porcini liquid and remaining 2 1/2 teaspoons rosemary. Cover and bake at 325° for 40 minutes or until a thermometer inserted in thickest portion registers 160°. Remove turkey rolls from pan; let stand 15 minutes. Cut each roll crosswise into 12 slices.
Strain cooking liquid through a fine mesh sieve over a bowl; discard solids. Combine 1/4 cup water and flour, stirring with a whisk until smooth. Return remaining cooking liquid to pan; add flour mixture, stirring with a whisk. Bring to a boil; cook 1 minute or until thickened, stirring constantly. Serve gravy with turkey.