FYI - I didn't put in the jalapeños or cilantro (I'm allergic to cilantro) and instead of Fritos I added more of the toasted corn tortillas crushed up on top. Also, I didn't have any cream so I used canned evaporated milk and it turned out great.
1. Adjust the oven racks to the upper-middle and lower-middle positions and heat the oven to 450 degrees. Lay the tortillas on two baking sheets, lightly coat both sides with cooking spray, and bake until slightly crisp and browned, about 12 minutes. Cool slightly, then break into bite-sized pieces. Using potholders, adjust the top oven rack to the middle position.
2. Melt the butter in a large Dutch oven over medium-high heat. Cook the onions, chiles, and cumin until lightly browned, about 8 minutes. Add the tomatoes with their juice and cook until most of liquid has evaporated, about 10 minutes. Stir in the flour and cook 1 minute. Add the cream and broth, bring to a simmer, and cook until thickened, 2 to 3 minutes. Stir in the chicken and cook until no longer pink, about 4 minutes. Off the heat, add the cilantro and cheese and stir until the cheese is melted. Season with salt and pepper to taste.
3. Scatter half of the tortilla pieces in a 13 by 9-inch baking dish set over a rimmed baking sheet. Spoon half of the filling evenly over the tortillas. Scatter the remaining tortilla pieces over the filling, then top with the remaining filling.
4. Bake until the filling is bubbling, about 15 minutes. Sprinkle the Fritos evenly over the top and bake until the Fritos are lightly browned, about 10 minutes. Cool the casserole 10 minutes. Serve.
Things you can do ahead of time: The casserole can be assembled through step 3 and refrigerated, covered with plastic wrap, for up to 1 day. When ready to bake, remove the plastic, cover the casserole with foil, and bake until the filling is bubbling, about 30 minutes. Remove the foil, top with the crushed Fritos, and proceed as directed with the rest of step 4.