Preheat oven to 350°F. Coat a 9x13-inch casserole dish with butter.
In a large bowl, stir together cream cheese, corn, creamed corn, and egg until combined.
Add onion, jalapenos, garlic powder, paprika, salt, melted butter, corn muffin mix, and 1 cup of cheddar cheese. Mix until combined.
Pour mixture into prepared dish, spreading evenly. Bake for 25 minutes.
Remove from oven, sprinkle remaining ½ cup of cheese on top and sliced jalapenos. Return to oven and bake for 10 more minutes, until cheese has melted and casserole has set.
Store in an airtight container for up to 3 days.If preparing a day ahead of time, wait to top with cheese and hold off on the second bake until the day of. Cover it with plastic wrap, and store in refrigerator. On the day, preheat oven to 350°F. Top casserole with cheese and sliced jalapenos, then bake for 10 minutes, until heated through.