Prepare crust: In a large bowl, add 1 1/2 cups flour, sage, baking powder and salt; stir with a fork to combine. Stir in buttery spread, mashing until mixture is crumbly. Add pumpkin purée and stir until flour is blended and mixture is clumpy. In bowl, use your hands to knead dough 5 to 8 times, just until dough comes together and is soft and slightly sticky, about 1 minute. (NOTE: Do not overwork dough. If dough sticks to bowl, add a bit more flour.) Place a layer of plastic wrap directly over top of dough and refrigerate until needed, 30 minutes or up to 1 day.
Prepare filling: In a large saucepan or Dutch oven, heat oil on medium-high. Add onion and sauté, stirring occasionally, until softened, about 5 minutes. Add carrots, celery, beans and corn; cook, stirring frequently, for 10 minutes or until slightly tender. Sprinkle 2 tbsp flour over top of vegetables, stirring to coat. Stir in milk, bring to a simmer and reduce heat to medium-low. Cook until milk thickens into a sauce and coats vegetables, 5 to 8 minutes. Stir in tarragon, salt, pepper and turkey and remove from heat.
Preheat oven to 375ºF. Coat a 9 x 13-inch baking dish with cooking spray. Spoon filling into dish in an even layer.
Transfer dough to a lightly floured work surface. Using a rolling pin dusted with flour, roll dough out to a 1/4-inch-thick, 9 x 13-inch rectangle. Set rolling pin at bottom edge of dough and gently roll dough onto pin so dough drapes over top. Lift rolling pin over baking dish and gently unroll dough over filling. Using a paring knife or kitchen scissors, trim excess overlapping dough from rim. If desired, crimp edges with the tines of a fork or your fingers. Cut 6 slits into crust to create steam vents. Transfer to oven and bake for 25 to 30 minutes, until filling bubbles and crust is lightly browned. Let cool for 5 minutes before serving.
Modern-day Italians serve cornmeal-based polenta as a simple side or hearty entrée, enriched with cheeses and herbs. Offering yet another take on the classic, our polenta is used to create a soft crust for a winter vegetable pie.
Lean ground turkey and buttermilk-mashed Yukon gold potatoes give this seasonal family favorite all the flavor and creaminess you'd expect from a shepherd's pie - with none of the actual butter or cream. Translation: a low-cal, low-fat meal sure to soothe any wintertime craving, guilt free.