Step 1: Preheat and Prepare
Preheat your oven to 350°F (175°C). Grease an 8×8-inch baking dish generously with butter or cooking spray. This prevents sticking and makes serving easier.

Step 2: Mix Dry Ingredients
In a medium bowl, whisk together the oats, baking powder, cinnamon, nutmeg, and salt. This ensures the leavening agent and spices are evenly distributed throughout the oats.

Step 3: Combine Wet Ingredients
In a large bowl, whisk together the eggnog, eggs, maple syrup, melted butter, and vanilla extract until smooth and well combined. The mixture should be creamy and slightly frothy.

Step 4: Combine Everything
Pour the dry ingredients into the wet ingredients and stir until just combined. Don’t overmix. If you’re adding any optional mix-ins like nuts or dried fruit, fold them in now.

Step 5: Transfer to Baking Dish
Pour the oatmeal mixture into your prepared baking dish. Use a spatula to spread it evenly and smooth the top.

Step 6: Bake
Bake in the preheated oven for 35-40 minutes, or until the top is golden brown and the center is set. A toothpick inserted in the center should come out mostly clean with just a few moist crumbs.

Step 7: Cool and Serve
Let the baked oatmeal cool for 5-10 minutes before slicing. This allows it to set up properly. Cut into squares and serve warm with your favorite toppings like whipped cream, maple syrup, or a sprinkle of cinnamon.