Cook the pasta: Bring a large pot of salted water to a boil. Cook pasta until just al dente. Drain, rinse briefly with cool water to stop the cooking, and shake off excess water.
Char the corn: Stovetop: Heat a large skillet over medium-high.
Add a splash of oil and the corn. Cook 5–7 minutes, stirring occasionally, until some kernels are lightly charred.
Grill: Grill whole ears over high heat, turning until charred in spots. Slice off kernels once cool.
Make the dressing: In a large bowl, whisk mayonnaise, sour cream, olive oil, lime zest, and juice.
Stir in garlic, chili powder, smoked paprika, cumin, 1/2 teaspoon salt, and several grinds of black pepper. Taste and adjust lime and salt.
Combine the base: Add cooled pasta and charred corn to the bowl with dressing. Toss gently to coat every piece.
Add the mix-ins: Fold in red onion, jalapeño, and most of the cilantro.
Add half the Cotija and toss again. Adjust seasoning with more salt, pepper, or lime if needed.
Chill: Cover and refrigerate at least 30 minutes, up to 24 hours. This helps the flavors bloom and the dressing set.
Finish and serve: Before serving, give it a stir.
If it looks tight, loosen with a splash of olive oil or a spoonful of sour cream. Top with remaining Cotija and cilantro. Add a final squeeze of lime and a pinch of chili powder for color.