For the vegetables, slice them all into a uniform width of ½”. Toss with olive oil and a sprinkling of salt and pepper. Lay them out on a single layer on a parchment lined baking sheet, and bake at 400°F for about 30 minutes or until tender.
In a small saucepan cook the sugar with 2 Tbsp water over medium-high heat, swirl pan occasionally, but do not stir. Brush sugar crystals that stick to the side of the pan down with a wetted pastry brush, or the mixture may seize if those crystals fall back into the mixture. Allow to boil until golden brown in color, about 7 minutes.
Remove from heat and add in vinegar and a pinch of salt, swirling pot to combine (will bubble up!), then quickly pour into a glass pie plate (tilting plate to cover the bottom completely). Sprinkle with rosemary and sage, then arrange roasted sweet/potatoes over caramel in a single layer, using the smaller pieces of carrot and parsnip to fill in the gaps. Sprinkle over the leeks, roasted garlic, parsley and cheese if using (tastes just as great without!).
Roll out the pastry and lay over top of pie plate, tucking edges of pastry down into pie plate (remember you’ll be flipping this over after its cooked). Prick all over with a fork and bake at 400°F for 20 minutes, then reduce to 350°F and cook for another 20 minutes until crust is golden.
Let cool about 3 minutes, then take a larger plate and place over top and flip. Watch through the glass plate until all the vegetables have dropped down before removing. Serve immediately.
Notes
Young parsnips do not need to be cored, however very large parsnips develop a fibrous, stringy and woody center that should be removed. To remove the core - quarter parsnip lengthwise, then cut out the center from each section.