While the oven is preheating, in a small pot, heat 1 tablespoon of olive oil on medium heat, add the finely diced onion and sauté for about 6-8 minutes until the onion gets soft and starts to turn colour.
Add the butter and let it fully melt.
Add the flour and mix with a spatula until all the flour is absorbed into the butter. The mixture will be dry and clumped up. This is exactly how it's supposed to be.
Constantly whisking, add the milk 1/4 cup at a time, making sure that the mixture is smooth after each addition.
Once all the milk is added, the mixture will be very thin. This is how it's supposed to be.
Cook on medium heat whisking occasionally for about 8-10 minutes until the mixture thickens. Watch the pot carefully as it goes from think to thick very quickly.
Meanwhile, cut the Lilydale® Oven-Roasted Carved Turkey Breast into bite-sized pieces.
Arrange the turkey in a 9-inch pie plate.
Add the frozen peas and carrots to the turkey and mix.
Pour the white sauce over the turkey mixture and spread around so that it covers all the turkey and vegetables.
Slightly roll the puff pastry so that it's big enough to cover the 9-inch pie plate.
Cover the pie plate with the puff pastry and trim the corners. Optionally, cut out decorative shapes from the scraps of puff pastry and arrange on top of the pot pie.
Poke a few holes in the pastry.
Place the pie plate on top of a parchment-covered sheet pan to catch accidental spills. Add the scraps of puff pastry to the sheet pan as you don't want to waste that yummy goodness.
Bake for 20-25 minutes. Depending on your oven, you might want to rotate the pie plate so that it gets golden evenly on all sides.