1. Preheat your oven to 350°F (175°C) and grease your chosen baking pan (8×8 or 9×13 inches).
2. In a bowl, pour boiling water over the rolled oats and let them soak for about 10-15 minutes to soften.
3. Add butter to the soaked oats and stir until melted.
4. Mix in sugar, eggs, and vanilla extract until well combined.
5. In a separate bowl, whisk together flour, baking soda, cinnamon, and optional nutmeg.
6. Gradually add the dry ingredients to the wet mixture, stirring until just combined.
7. If desired, fold in extras like raisins, chocolate chips, or chopped nuts.
8. Pour the batter into the prepared baking pan and spread it evenly.
9. Bake for 30-45 minutes, or until a toothpick inserted in the center comes out clean.
10. While the cake bakes, prepare the topping by combining butter, brown sugar, milk or cream, shredded coconut, and chopped nuts in a small saucepan.
11. Heat the topping mixture over medium heat until the butter is melted and everything is well combined.
12. Once the cake is baked, remove it from the oven and set the oven to broil.
13. Spread the topping evenly over the warm cake.
14. Place the cake under the broiler for 1-2 minutes, watching closely until the topping is golden and bubbly.
15. Remove the cake from the oven and let it cool slightly before slicing.
16. Serve warm or at room temperature, as a snack, dessert, or even breakfast.