Preheat oven to 350°F and adjust oven rack to middle position. Spray a 9-inch round cake pan with nonstick baking spray (I used the Nordic Ware Charlotte Cake Pan).
Place oats and butter in a large bowl and pour boiling water on top. Stir, cover and let the oatmeal mixture stand 20 minutes.
1 cup quick oats, ½ cup unsalted butter, 1¼ cups water
In a separate medium bowl, whisk the flour, baking soda, salt, nutmeg, apple pie spice, and cinnamon together.
1⅓ cup all-purpose flour, 1 teaspoon baking soda, 1 teaspoon kosher salt, ¼ teaspoon freshly grated nutmeg, 1 teaspoon apple pie spice, 1 teaspoon ground cinnamon
After the oatmeal mixture has rested 20 minutes, add granulated sugar, brown sugar and eggs; stir until incorporated.
1 cup granulated sugar, 1 cup dark brown sugar, 2 large eggs
Add flour mixture to the wet ingredients and mix just until the flour in incorporated.
Pour mixture into the prepared pan and bake at 350°F for 40-50 minutes or until a toothpick inserted in the middle comes out clean.
While the cake bakes, make the frosting. Beat the butter, cream, sugar, and salt together in a medium saucepan set over medium heat. Bring to a boil and cook 15 seconds.
6 tablespoons unsalted butter, ¼ cup heavy cream, ½ cup granulated sugar, ¼ teaspoon kosher salt
Remove from the heat and add coconut, pecans, vanilla, and lemon juice. Mix well.
½ cup sweetened shredded coconut, 1 cup chopped pecans, 1 teaspoon pure vanilla extract, 1 tablespoon freshly squeezed lemon juice
Reheat and stir the frosting to warm right before pouring over the warm cake.
Remove the cake from the oven and pour the warm frosting over the top. Spread out the frosting to cover the entire cake.
The cake can be served after 15 minutes (delicious with a scoop of ice cream) or served cold. I love it both ways.
Allow cake to cool completely before covering for storage.