Boil macaroni in salted water according to package directions. Once cooked, drain the macaroni and place back into the pot, leaving it off the heat to cool down.
Melt butter in a skillet over medium heat. Add onions, cook until softened and slightly caramelized. Scrape the onions and melted butter into the pot with the macaroni. Stir to combine.
In a large bowl, beat eggs until fluffy. Add evaporated milk, salt, pepper, garlic powder, dry mustard, dried thyme and cayenne pepper. Stir to combine.
Pour the egg mixture over the macaroni and stir until well coated.
Stir in 3 cups of the shredded cheese.
Pour into the greased baking dish and top with reserved ½ cup of shredded cheese.
Bake until the pie is firm, and the top is golden brown. About 35-40 minutes.
Allow pie to rest for 10-15 minutes before serving.
Notes
Baking Dish Size: I used a 9" x 11" enamelled cast iron baking dish to test this recipe. If you don't have that size, a 10" x 10" baking dish will also work. You can use a standard 9" x 13" baking dish, but your pie may turn out a little bit thinner than mine.
Cheese Selection: This dish is traditionally made with Trinidad-style cheese (New Zealand cheddar), but you can use any cheddar you like, or use a mixture of cheddar and mozzarella. Aged cheddar will taste more "cheesy" than mild cheddar. Avoid pre-shredded cheese; it contains anti-caking agents that affect texture.
Shredding Tip: Cold cheese is easier to shred than warm cheese. Keep it in the fridge until ready to use.
Evaporated Milk is Essential: Do not substitute with regular milk—it will curdle at high temperatures. Evaporated milk stays stable when baked.
Egg Adjustment: Use 1 egg for a lighter texture, 2 eggs for a richer, more custardy pie. Two eggs create a firmer, more sliceable result.
Onion Options: For onion flavour without cooking, substitute 1 teaspoon onion powder. Raw grated onion is too sharp for this recipe.
Pepper Choice: White pepper keeps the pie visually clean with no black flecks. Black pepper works fine and tastes nearly identical.
Mustard Flexibility: Dry mustard powder, yellow mustard, or Dijon all work well. Use whatever you have on hand.
Prevent Over-Browning: If the cheese on top begins to brown too quickly, cover it with tin foil for the remaining baking time.
Don't Overbake: Pie should be just set in the center with a slight jiggle. It continues cooking as it cools. Overbaking makes it dry.
Resting Time: Let the pie rest 10-15 minutes after baking for the easiest slicing and best texture.
Make Ahead: Assemble up to 1 day ahead and refrigerate covered. Add 5-10 minutes to the baking time if starting from cold.
Storage: Refrigerate leftovers in an airtight container for up to 3 days. Reheat individual portions in the microwave or the whole pie in a 350°F oven until warmed through.