Pour the heavy cream evenly over the top of the corn, then sprinkle the kosher salt over everything. Gently stir just enough to tuck the butter and cream cheese slightly down into the corn while keeping the corn mostly in an even layer.
Cover the casserole dish tightly with foil to help the sauce get hot and bubbly without drying out. Place the dish in a cold oven, then set the oven to 350°F (175°C).
Bake for 30 minutes, then carefully remove the foil and give the corn a good stir, scraping the corners and bottom so the melted cream cheese and butter mix into the cream and coat every kernel.
Return the dish to the oven, uncovered, and bake for another 15–20 minutes, stirring once more halfway through, until the sauce is thick, silky, and bubbling gently around the edges and the corn is tender. The overall look should be a rich, creamy base with bright yellow kernels peeking through.
