Turn the Instant Pot to the sauté setting and heat 2 tablespoons of oil. Cook onions and garlic for 2-3 minutes until translucent, then add mushrooms and a pinch of salt. Sauté for an additional 3-4 minutes until golden brown.

Stir in chopped carrots, diced celery, dried thyme, soy sauce, tomato paste, and half a cup of broth or water. Mix until well combined and cancel the sauté mode.

Insert a steamer basket into the Instant Pot and add cubed potato and cauliflower. Secure the lid, set the pressure valve to sealing, and cook on high pressure for 9-10 minutes.

Allow pressure to release naturally for 10 minutes, then release any remaining steam. Remove the steamer basket and set the pot to sauté. Mix cornstarch with broth to create a slurry and stir into the sauce until thickened, about 2-3 minutes.

Mash steamed potato and cauliflower in a mixing bowl. Add olive oil, non-dairy milk, salt, and pepper, mashing until creamy and smooth.

Serve the Vegan Mushroom Bourguignon layered over the creamy mash. Garnish with fresh herbs like thyme or parsley.