For the chicken and pasta: Remove 4 to 5 chipotle peppers and a bit of adobo sauce from the can and rub it all over the chicken; measure out 2 tablespoons of the adobo sauce and set aside for later (reserve any remaining chiles and adobo sauce from the can for another use). Rest the chicken in a bowl or on a plate for 2 hours total, refrigerated first for 1 1/2 hours, then at room temperature for an additional 30 minutes.
In a large pot, add the garlic, chicken and the chipotle peppers from the marinade. Add just enough water to cover, then bring to a boil on medium high. Once boiling, turn the heat to the lowest setting and poach the chicken until cooked through, about 15 minutes. Remove the chicken to a plate and rest (reserve the poaching water for cooking the pasta). Fish out the peppers and discard them; place the garlic cloves in a large bowl and smash them with the back of a spoon or your hands. Once the chicken is cool enough to touch, shred it by hand into bite-size pieces.
Preheat the oven to 375 degrees F. Use the butter or cooking spray to coat the bottom and sides of a 13-by-9-inch casserole dish.
In the same pot used to poach the chicken, add more water to the poaching water and a nice pinch of salt and bring the pot back to a boil (watch the water; it may foam up a bit from the poaching process). Add the pasta and cook 1 minute less than the package suggests. Drain the pasta in a colander.
For the sauce: In the large bowl with the garlic, add the heavy cream, cheese, crema, flour, pepper, scallions, eggs, reserved 2 tablespoons adobo sauce, shredded chicken and cooked pasta. Stir to combine. Pour into the prepared dish.
For the topping: In a medium bowl, toss together the crushed chips and cheese. Sprinkle this mixture evenly over the dish. Bake, uncovered, until golden brown on top, about 30 minutes.
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