For vinaigrette, whisk together mustard, shallots, maple syrup, vinegar, salt, pepper and 1 tablespoon water in a small bowl. Slowly whisk in both oils until emulsified. Adjust seasoning if desired. Store the dressing, covered, in the fridge for up to 1 week.

Remove outer leaves from Brussels sprouts and discard any that are blemished. Remove stems with a knife and peel the leaves. As you peel away leaves, you may need to cut the stem again to better access the leaves.

Heat a large skillet over medium-high heat and add chorizo, stirring occasionally, until fat starts to render and chorizo is crisp, about 5 minutes. Transfer chorizo to a bowl and wipe skillet clean.

Heat skillet over medium-high heat and add ghee. Working in batches, add Brussels sprout leaves, tossing and letting them wilt slightly before adding more. Add salt and pepper and cook, stirring occasionally, until golden and slightly crisp, 7 to 8 minutes.

When almost done, push the leaves to the edges of pan to clear a small circle in the middle. Add hazelnuts to slightly toast, then add sliced garlic and cook for 45 seconds. Return chorizo to the pan along with 2 tablespoons of the vinaigrette. Toss to combine and transfer to a serving platter, drizzling with more of the maple vinaigrette if desired.