Wash and dry all produce. Slice corn kernels off cob; discard cob. Dice tomato. Halve, peel, and mince shallot. Zest and quarter lime (quarter both limes for 4 servings). Roughly chop cilantro leaves and stems.
Heat a drizzle of oil and 1 TBSP butter (2 TBSP for 4 servings) in a large pan over medium-high heat. Add corn and cook, stirring occasionally, until corn is tender and lightly charred, 4-6 minutes. (TIP: If corn begins to pop, cover pan.) Season with salt and pepper. Turn off heat; transfer to a medium bowl. Wipe out pan.
Meanwhile, in a small bowl, combine sour cream and lime zest. Add water, 1 tsp at a time, until mixture reaches a drizzling consistency. Season with salt and pepper.
Pat chicken dry with paper towels and season all over with salt, pepper, and Southwest Seasoning. Sprinkle with ¼ tsp ancho chili powder (½ tsp for 4 servings; we sent more). Heat a drizzle of oil in pan used to char corn over medium-high heat. Add chicken and cook, stirring occasionally, until browned and cooked through, 5-6 minutes.
To bowl with corn, stir in tomato, cilantro, lime juice (to taste), and a few pinches of shallot (to taste; add more if you like). Season with salt and pepper. If you like spicy food, add a pinch of remaining ancho chili powder (to taste).
Finish and Serve
Wrap tortillas in damp paper towels and microwave on high until warm and pliable, about 30 seconds. Divide warmed tortillas between plates and fill with chicken and corn salsa and drizzle with crema. Serve with remaining lime wedges on the side.