• Grease a 9 x 13-inch baking dish with olive oil. Preheat oven to 400°F (200°C).
• In a non-stick saucepan, over medium heat, melt vegan butter and cook onion and garlic, stirring often, until translucent and fragrant - about 3 minutes.
• Stir in the flour. It will form a 'roux' which looks like a paste.
• Gradually add vegetable stock, whisking at the same time to incorporate, then gradually add soy milk, thyme, salt, nutmeg, pepper, and nutritional yeast. Keep whisking slowly to combine.
• Stop whisking, bring to a simmer (don't boil!) and keep cooking, occasionally whisking until the sauce slightly thickens - about 2-3 minutes. It should form small bubbles on the sides of the saucepan, not boil. The sauce shouldn't be thick as bechamel. It's creamy but more liquid than bechamel. Taste, add more nutritional yeast, up to 2-3 extra tablespoons for an intense cheese flavor.
• Place half of the sliced potatoes in the prepared baking dish, pour half the sauce, add the remaining potato slices, and top with the remaining cheese sauce.
• Cover the pan with foil and bake for 30 minutes until sauce forms bubbles on the sides of the pan.
• Remove foil, add the cup of vegan shredded cheese all over the pan and keep baking uncovered for another 25-30 minutes until the potato slices are tender.
• Serve with fresh rosemary or fresh thyme.

Storage

• Store leftovers in the fridge for up to 4 days in a sealed container or freeze them in a sealed box for up to 3 months. Thaw in the refrigerator the day before serving.