Before starting, preheat the oven to 425°F.Wash and dry all produce. Strip 2 tsp (4 tsp) thyme leaves from stems, then finely chop. Peel, then cut potatoes into 1/2-inch pieces. Add potatoes, 2 tsp salt and enough water to cover (by approx. 1 inch) to a large pot (use same for 4 ppl). Cover and bring to a boil over high heat. Once boiling, reduce heat to medium. Simmer uncovered until fork-tender, 10-12 min.

Return the same pan to medium-high. Add 1 tbsp (2 tbsp) butter, then mirepoix. Season with salt and pepper. Cook, stirring occasionally, until veggies soften slightly, 2-3 min. Add half the thyme. Cook, stirring often, until fragrant, 30 sec.

Add bison to the pan with veggies. Cook, breaking up bison into smaller pieces, until no pink remains, 4-5 min.** Season with pepper. Add tomato sauce base, stock powder, flour, 1 tsp (2 tsp) vinegar and 1/4 tsp (1/2 tsp) sugar. Cook, stirring constantly, until combined, 1 min. Stir in peas and 3/4 cup (1 1/2 cups) water. Bring to a simmer. Once simmering, cook, stirring often, until sauce thickens slightly, 1-2 min. Season with salt and pepper, to taste.

Transfer bison filling to an 8x8-inch baking dish (same for 4 ppl). Drain and return potatoes to the same pot, off heat.Mash 2 tbsp (4 tbsp) butter into potatoes until creamy. Season with salt and pepper.Top filling with mashed potatoes. Smooth mashed potatoes over top, covering filling.

Place baking dish on a baking sheet. Bake in the middle of the oven, rotating the dish halfway through, until potatoes are golden-brown, 8-10 min. Meanwhile, halve grapes. Add remaining vinegar, 1/8 tsp (1/4 tsp) sugar and 1 tbsp (2 tbsp) oil to a large bowl. Season with salt and pepper, to taste, then whisk to combine.

Allow pie to cool for 3-5 min before serving. Meanwhile, add grapes and arugula and spinach mix to the bowl with vinaigrette, then toss to combine. Sprinkle seed blend over salad.Divide pie between plates. Serve salad alongside.