Melt the butter in a skillet over a medium heat. Thinly slice the leeks and add to the skillet along with the diced pancetta. Cook through until the pancetta is golden and the leeks are tender. Set to one side to cool.
Preheat the oven to 400 degrees Fahrenheit. Add the cream cheese, mayonnaise, sour cream, grated cheddar, parmesan, lemon zest, garlic powder, salt and pepper to a large mixing bowl. Beat together well to combine.
Spoon the cooked pancetta and leeks into the bowl. Mix together until well combined. The pancetta and leeks should be evenly distributed throughout the cheese mixture.
Select a small oven proof dish. Spoon the dip into the dish. Level the dip with the back of a spoon to ensure that it bakes evenly throughout.
Transfer to the oven to bake for 18-20 minutes. The dip should be hot through and the cheese should be melted and golden on top. Serve warm.