Heat large skillet or saucepan over medium heat. Once hot, add butter and let it melt and start to sizzle - about 1 minute.
Add minced garlic and serrano pepper and stir. Cook for 1-2 minutes, stirring frequently, then turn down heat if garlic starts to brown too quickly.
Add flour 1 Tbsp at a time and whisk (see notes for flour-free version).
Cook for 1 minute, then whisk in almond milk ½ cup (120 ml) at a time until it no longer looks thick and gloppy - about 1 ¾ cups total (amount as original recipe is written // adjust if altering batch size).
Cook in skillet for 2 minutes, whisking frequently. Then transfer to high speed blender. Add nutritional yeast, salt, cumin, half of the green chilis (2 Tbsp as original recipe is written // adjust if altering batch size), sweetener of choice, and hot sauce (optional). Blend on high until creamy and smooth.
Taste and adjust seasonings as needed, adding more nutritional yeast for extra cheesiness, salt for savoriness, or sweetener for flavor balance.
Transfer back to skillet or saucepan and simmer on low for 5 minutes, whisking or stirring often, to thicken.
Turn off heat and add remaining green chilis (2 Tbsp as original recipe is written // adjust if altering batch size). Stir to combine. Garnish with red pepper flakes and fresh cilantro (optional). Enjoy with chips, or atop Mexican dishes, such as nachos, enchiladas, or tacos!
Store leftovers in a glass jar or container in the refrigerator up to 4-5 days. Reheat in the microwave or in a small saucepan over medium heat. Best when fresh.
*In place of flour, you can sub arrowroot starch or cornstarch to keep this recipe gluten-free. I find the consistency to be not quite as creamy, but it still works! *Nutrition information is a rough estimate calculated without optional ingredients.