Bring a large saucepan of lightly salted water to a boil. Add the corn kernels and boil for 6 to 7 minutes. Drain. Transfer to a plate to cool. Preheat the oven to 350°F. Butter a 9x5-inch loaf pan and line it with parchment paper, if using. Set aside. Empty the corn bread mix into a large mixing bowl. Add the sour cream, butter, and egg and whisk until smooth. Stir in the corn kernels. Scrape the batter into the prepared pan and bake on the center oven rack for 40 minutes, until the top is golden brown and a tester inserted into the center of the bread comes out clean. Transfer the pan to a rack to cool. Serve warm or at room temperature.