Add the oil to a sauce pan and place it over medium heat. Saute the onion, jalapeno, and garlic until soft--3-5 minutes.
Add the red pepper, tomato paste, vinegar, sugar, cumin, stock and 1/4 tsp salt. Simmer for 10 minutes on low.
Remove from heat and carefully pour into a blender. Add the cream and place the lid on the blender--sightly jarred so it can vent. Puree the sauce until smooth, then set aside.
For the Shrimp Tacos:
Sprinkle the raw shrimp with salt pepper and paprika. Place the corn and the shrimp on the grill. Grill the shrimp for 2 minutes per side, until just pink. Grill the corn for 2 minutes per side, rotating to get char marks on all sides. When the corn has cooled a little, cut it off the cobs.
Warm the tortillas in the microwave. Place a bed of cabbage on the bottom of a tortilla, followed by 3-4 shrimp, corn, grapes and avocado. Drizzle with ranchero sauce and serve.