Preheat the oven to 350°F (175°C). Grease the baking pan with butter and set aside.
In a large mixing bowl, combine the softened cream cheese and sugar using a hand or stand mixer until the mixture is smooth, creamy, and slightly fluffy, with no visible lumps.
Add the eggs one at a time, mixing well after each addition. Observe the mixture becoming slightly thicker and more homogeneous. Stir in vanilla extract, citrus zest, and melted butter until evenly incorporated.
Gradually add the flour to the wet mixture, mixing on low speed just until combined. The batter should be thick and smooth, with a slightly lumpy texture from the citrus zest.
Pour the batter into the prepared baking pan, smoothing the top with a spatula. Place in the oven and bake for about 30 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out with moist crumbs.
Remove the cake from the oven and let it cool in the pan for 10 minutes. Transfer to a cooling rack and allow to cool completely before serving, observing the cake's dense, velvety crumb structure.