Preheat the oven to 425 degrees.

Place the sweet potatoes on a baking sheet lined with parchment paper. Drizzle olive oil over the sweet potato, and season generously with kosher salt.

Bake until very soft and tender.

Gently heat the plant milk until just warm.

Place the orange zest and miso into the milk, and mix to combine.

Place the hot sweet potatoes into a large bowl. Using a potato masher start to mash the sweet potatoes. Add the warm plant, and continue to mash until smooth.

Add additional plant milk if needed, a large whisk is a handy way to mash and whip simultaneously.

Finish with a dash of olive oil and salt.

Combine the light brown sugar, flour, and nutmeg in a large bowl.

Cut the cold vegan butter into the flour mixture, and continue until a cornmeal texture is reached. It is okay if a few large clumps of butter are present.

Add the walnut piece, and stir to combine.

Keep cold until it's time to cover the sweet potato puree.

Preheat the oven to 375 degrees.

Drizzle a light layer of oil on the bottom of 12 inch cast iron pan.

Spread the sweet potato pure in the pan.

Evenly spread the walnut crumble over the top.

Cook until the crumbs is crispy and golden brown, about 30 minutes.

Sprinkle the mini marshmallow over the top and brown under the broiler. This happens fast to stay alert.