Pre-heat oven to 350°F.
Melt butter in a 10-inch cast-iron skillet over medium-high.
Add onion, Italian seasoning, salt, garlic powder, and pepper to pan; sauté 5 minutes.
Reduce heat to medium; cook until onions are almost tender, about 5 minutes; stirring frequently.
Stir in cream cheese until melted; stir in mayonnaise and sour cream.
Gradually add cheddar and gouda; stirring until cheeses melt.
Place the skillet in the pre-heated oven and bake until dip is bubbly and starting to brown on top; 10 to 12 minutes.
Serve warm with potato chips or crackers.