Peel and seed the poblano peppers. Toss the peppers, avocado, cilantro, two cloves of garlic, Crema Mexicana and chicken stock powder in a blender and blend until smooth. The mixture should be thick but not too thick to pour. If needed, thin out by adding more Crema. Use the chicken stock to add saltiness (if needed), but keep in mind the shrimp and cheese will add salt so the sauce should be slightly under-salted.
Next, sauté the shrimp in butter with the remaining sliced garlic clove. Once the shrimp is pink, transfer it to a shallow oven-safe dish. Sprinkle some shredded cheese over the shrimp and then cover the shrimp with the sauce. Add a generous layer of cheese over the top and then place in a pre-heated 350 degree oven for about 10-15 min or until the cheese is completely melted and the edges of the sauce begin to bubble. Serve with warmed flour tortillas.