Possible Clues:

• Really thick fog, metaphorically
• Heavy fog
• Change in Mexico to eat a revolting dish
• Dish like old London fog
• Fog, so to speak
• Thick 4-Across metaphor
• Liquid vegetable-based dish (like thick fog)
• *Metaphor for dense fog
• Dish found near front of a menu that's pretty impenetrable
• Andersen's Buellton attraction