Chile Shrimp with Brussels Sprouts and Lemon Aioli

Ingredients

• 1 pound new baby potatoes
• Fine sea or table salt
• Olive oil
• 1/2 pound Brussels sprouts (about 40 small), thinly sliced or shredded (see NOTES)
• 1/2 teaspoon Aleppo pepper or any chile powder
• 1/2 teaspoon crushed red pepper flakes, divided (optional)
• 1 teaspoon garlic powder
• 1 1/2 tablespoons salted butter, cut into small pieces
• 1/2 pound peeled, deveined medium shrimp (40-50 count), thawed if frozen
• Fresh flat-leaved parsley leaves and tender stems, chopped
• 3/4 cup mayonnaise
• 1 preserved lemon (about 1 ounce) pith and innards discarded, finely chopped (see NOTES)
• large garlic clove, minced or finely grated
• Finely grated zest of 1 large lemon, plus wedges for serving