Preheat the oven to 400°F.
In the bowl of a stand mixer fitted with the paddle attachment, combine the cream cheese, mayonnaise, onions, Parmesan cheese, jalapeño (optional), chives and black pepper. Beat until combined. (Alternately, combine all ingredients in a bowl and stir until combined.)
Transfer the dip into a 9- or 10-inch baking dish, smoothing it into an even layer.
Bake the dip until it is dark golden brown on top and bubbly, about 25 minutes.
Remove the dip from the oven and serve with toasts or veggies for dipping.
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