Gardener's Cottage Pie - Testing

If shepherds were vegetarian, what would they make their pies from? This is a recipe I'd started exploring about 5 years ago and lost the finalized instructions for. The following are the ingredients, I think...
1 - It needs something. After the fact, I added cheddar, which worked nicely. I'm also wondering how mushrooms would change things, and if it's a question of cheddar OR mushrooms, or a matter of cheddar AND mushrooms.

2 - It's been sooo long since I've made this recipe. In the intervening years since, I feel like I may have learned something that could help with this recipe. Simply put - brown the veg. I will indicate this in the recipe for when I make it tonight. Oh, and it's late fall, I have no zucchini, so I'm going to put in some winter squash instead. I know, lots of variables, but also I want to use what's on hand and seasonal.

The cooking was interesting. The sequencing is pretty good but I'm putting the mushrooms with the carrots and squash.

3 - 2025-05-23 It all works really well but the topping is a bit stodgy. I recently discovered a topping that is creamy and light and fluffy when I made the Hachis Parmentier, which I'd like to try with this dish. 

Topping
1½ lbs. boiled, peeled and mashed potatoes 
2 Tbsps. butter
2 Tbsps. cream
salt, to taste
OPTIONAL dash of turmeric 

1. Mash all together until well blended

1 kg/2.2lbs potatoes, peeled and cut in half or quarters

3/4 cups milk

50g butter

2 egg yolks

1 pinch nutmeg

1. Boil the potatoes in salted water, about 20 minutes. 
2. Mash the potatoes along with the butter, milk, egg yolk and nutmeg.

Filling

3 Tbsps. veg oil

2 onions, diced (12oz/340gr)

1 leek (6oz/170g) sliced
4 garlic cloves, minced (20gr)
2 carrots, diced (6oz) 

8 oz mushrooms diced

OPTIONAL: 8oz winter squash, small dice, fall/winter
½ cup white wine
1 red bell pepper, diced
OPTIONAL 3 stalks (about 4.5 oz) diced celery (OR a hefty pinch of celery seed)
1 large tomato or 8oz diced canned tomato
1 cup corn

1 cup peas 
1 bunch spinach or swiss chard, sliced thin
OPTIONAL: 1 zucchini, diced in summer
½ tsp pepper
1 tsp paprika

1 tsp basil

1 tsp thyme

1 tsp hot sauce

½ tsp salt

1 cup (4oz) grated cheddar
Hot sauce, to serve

1. While the potatoes are boiling, sauté onion, leeks and garlic in the oil until starting to brown.
2. Add the carrots, mushrooms and squash and sauté until they start to brown, then add wine. 
3. Scrape up the loosened fond and cook the veg until tender.
4. Add the pepper and the tomato and cook a bit longer.
5. Toss in the corn, peas, spinach and zucchini. Do not cover (to concentrate flavor) and cook for about 5 minutes or until the liquid has reduced a bit (how much?).
6. Mix in the cheese, salt, pepper, paprika, basil, thyme, and hot sauce.
7. Spoon into a casserole and top with the potato mix.
8. Bake 30 minutes at 400°F.