Preheat oven to 400 degrees F. Bring a large pot of salted water to boil. Add trimmed Brussels sprouts and cook for 6 minutes. Drain Brussels sprouts and rinse with cold water. Transfer to medium bowl and set aside.

In small blender or food processor, combine cashews, nutritional yeast, garlic and basil until mixture becomes fine and crumby.

In small saucepan, melt buttery coconut oil. Whisk in rice flour until fully incorporated and smooth. Slowly whisk in almond milk, nutmeg and salt, stirring until mixture is smooth and creamy. Add siracha, if using. Whisk in ½ the cashew mixture.

Pour sauce over Brussels sprouts and stir to combine. Transfer mixture to 2.5-quart casserole dish. Spread out evenly.

In small bowl, combine remaining cashew mixture with panko crumbs and sprinkle on top of casserole. Drizzle olive oil evenly on top of crumb mixture.

Bake casserole for 20-30 minutes until golden brown and bubbly.