Preheat your oven to 400 degrees F. Spray a 2-quart baking dish with olive oil.
Place the Brussels sprouts in a large microwave-safe bowl. Add ¼ cup water. Cover and microwave on high until tender-crisp, about 6 minutes.
Meanwhile, in a small bowl, mix together the sour cream, mustard, kosher salt, black pepper, garlic and grated gruyere.
Drain the Brussels sprouts and return to the bowl. Add the cheesy sour cream mixture and toss to coat.
Transfer the coated Brussels sprouts to the prepared baking dish. Mix together the grated Parmesan and pork panko and sprinkle them on top. Lightly spray with olive oil.
Bake the casserole until golden brown and bubbly around the edges, about 15 minutes. Serve immediately.
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Notes
Variations:
You can use mayonnaise instead of sour cream or use a mix of both. Softened cream cheese is also good.
Instead of Gruyere, you can try using shredded cheddar or provolone.
A pinch of dried thyme is a nice addition to this casserole.
Instead of crushed pork rinds, you can sprinkle the finished casserole with bacon bits.