Step 1In a large, heavy-bottom saucepan, heat the olive oil over medium high heat, then add the onions, jalapeno and garlic and cook until caramelized, about 10 minutes, stirring frequently. Stir in the white wine and cook until the wine reduces by half, 2 to 3 minutes. Stir in the heavy cream and cook over high heat until the liquid reduces by half, about 10 minutes.
Step 2Remove from heat and stir in the cilantro. Blend the sauce using a stand or immersion blender, then strain. Season to taste with salt and pepper. If desired, adjust the heat with Tabasco and brighten with a little lemon juice. This makes about 2 cups sauce. The sauce will keep, refrigerated, up to 2 days.
Step 1Brush each side of each mahi-mahi with olive oil and season with a pinch each of salt and pepper. Grill the fish over medium-high heat until firm and opaque on each side, 2 to 4 minutes (timing will vary depending on the thickness of the fillets). Plate the grilled fish, dividing the sauce among each serving. Serve immediately.