Sprinkle the cornstarch over the cheeses in a large bowl and toss to coat.
Heat the butter and vegetable oil in a large skillet over medium high heat.
Add the jalapeños and sauté for 5-10 minutes, until soft. Remove the jalapeños to a plate.
Carefully add the milk, slowly so it doesn't sputter everywhere while whisking until completely combined with the butter. Remove from heat and stir in the cheeses until smooth and melty.
Season with salt to taste and stir in most of the corn, reserving some for the top.
To serve, place the reserved corn on top, drizzle with crema if desired, cilantro, queso fresco or cotija and chili powder. Serve warm with chips!
