Cooking Steps
Preheat oven to 300º.
On a baking sheet, spread crumbled cornbread and bake until slightly dried and crispy, about 25 minutes. Let cool.
In a large pot over medium heat, heat 2 tablespoons oil until shimmering.
Add crushed red pepper flakes and half of garlic, minced and divided. Cook, stirring, until fragrant, about 2 minutes.
Add dry white wine and bring to a simmer.
Carefully add mussels to pot and immediately cover. Cook, lightly and occasionally shaking pot, until some mussels open, about 4 minutes.
Transfer any open mussels to a large bowl. Cover pot and continue to cook until most mussels are opened, about 2 minutes more; discard closed mussels.
Transfer remaining mussels to bowl and refrigerate until ready to use.
Reserve ½ cup mussel stock, then wipe out pot.
Heat remaining oil over medium heat until shimmering.
Add finely chopped onion and cook, stirring occasionally, until just beginning to sweat, about 2 minutes.
Add inely chopped Spanish chorizo and cook, stirring often, until some fat is rendered and chorizo has slightly crisped up, 5 to 6 minutes.
Add remaining garlic and cook, stirring, until fragrant, about 2 minutes more.
Transfer chorizo mixture to a large bowl. Add cornbread crumbs, finely chopped fresh parsley leaves, and ¼ cup reserved mussel stock. Toss, adding more stock 1 tablespoon at a time if needed, until mixture is slightly wet and moldable.
Line a baking sheet with crinkled foil (this will allow the mussels to stand up).
Remove top shells of mussels, leaving meat in the other half.
Using a spoon, fill mussels with cornbread filling, then arrange on prepared sheet. Drizzle mussels with extra-virgin olive oil.
Set a rack 6” below broiler. Broil mussels, shifting sheet as needed to ensure even cooking, until beginning to brown and are heated through, about 4 minutes.
Using tongs, transfer mussels to a platter.
Top with finely chopped fresh parsley leaves and serve.
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