1 puff pastry sheet from a 450 g pkg pre-rolled frozen puff pastry or 2/3 of 397 g pkg frozen puff pastry, thawed
1 egg, whisked (optional)
To cook your own chicken, half fill a large saucepan with water and bring to a boil. Add chicken. Cover and adjust heat so it simmers 30 minutes if using chicken pieces or 1 hour for a whole chicken. Drain and run under cold water to stop the cooking.
While chicken cooks, slice onion into quarters through the stem end. Place cut side down on a cutting board and thinly slice. Coarsely chop fennel. You should have about 3 cups (750 mL). Coarsely chop red pepper. It should measure about 2 cups (500 mL).
Melt butter in a large wide saucepan. Add onion, separating into pieces as you add, then fennel and peppers. Stir often over medium until fennel starts to soften, about 10 minutes. If vegetables begin browning, reduce heat.
Evenly sprinkle flour over vegetables. Stir constantly over medium for 3 minutes, scraping the bottom of pan often. Stir in wine, cream, dried basil, sage and salt. Stir constantly until very thick, about 2 minutes. Scape pan bottom often. Stir in Alfredo sauce and fresh basil. Remove from the heat.
Remove skin and bones from chicken, then cut into large bite-size pieces. They should measure about 4 cups (1 L). Stir into the creamy filling. Remove chicken from the skin and bones, cut into large bite-size pieces. They should measure about 4 cups (1 L). Stir into the filling. If making the pie right away, stir gently over medium until chicken is hot. If making ahead, cover and refrigerator up to 2 days.
The ideal baking dish is one where the filling comes right up to the top of the dish. This filling makes about 8 cups (2 L) which will fill most rectangular or oval dishes about 11 inches (27.5 cm) long. Turn filling into the dish and roughly smooth the top.
On a lightly floured surface, using a lightly floured rolling pin, roll out the pastry sheet or block of pastry until it is about 2 inches (5 cm) larger than the baking dish you are using. If using a pastry sheet, roll just enough to match the shape of the top of the baking dish and then extend it by about 2 inches (5 cm).
Carefully pick up pastry and lay over filling. Gently press down over filling. Fold in overhanging edges leaving enough edge to press onto the rim of the dish. Make 3 or 4 slits in the middle of the pastry for steam to escape. To help browning, lightly brush pastry with egg. Bake in centre of 375°F (190°C) oven until pastry is golden brown and filling bubbly. This will take about 45 minutes to 1 hour. Let sit 10 minutes to give sauce a chance to thicken before serving.