Heat the oven to 350°F. Melt the butter or heat the neutral oil in a small skillet over medium heat, then cook the finely diced onion for 4–6 minutes until soft without letting it brown heavily.

In a mixing bowl, stir together the softened cream cheese, ranch dressing, Buffalo sauce, and 1/2 cup of the shredded cheddar until mostly smooth. Add the shredded chicken, sautéed onion, and optional blue cheese, mixing until evenly combined.

Transfer the mixture to an 8-inch square baking dish, 9-inch pie plate, or similar small casserole dish. Spread it into an even layer so the center and edges warm at the same rate.

Sprinkle the remaining 1/2 cup shredded cheddar over the top. Bake uncovered for 20–25 minutes, until the dip is bubbling around the edges and fully melted in the center.

Let the dip rest for 5 minutes before serving so it thickens slightly and is easier to scoop. Finish with optional green onions, blue cheese, extra cheddar, or a drizzle of ranch.