Preheat oven to 400 F.
Melt butter in a saute pan over medium.
Add the onions and season with salt. Cook for 2 to 3 minutes or until translucent.
Add the garlic and cook until fragrant.
Add the spinach and toss to combine with onions.
Drizzle the anise liquor over spinach and cook until wilted.
Remove pan from heat and stir in bread crumbs, cheese and hot sauce. Adjust seasoning to taste.
Place a heaping tablespoon of spinach mixture on top of each oyster and arrange on a baking sheet lined with rock salt.
Bake for 6 to 8 minutes or until light golden on top.
Serve warm with a glass of cold champagne.
