Preheat the oven to 350 F/180 C. Line three 8-inch cake pans with parchment paper on the bottoms and set them aside.

Bring a pot of water to a boil. Add in the oats, stir, and remove the pot from the heat. Cover the pot for 20 minutes. Let the oatmeal cool to room temperature before using.

Whisk together the flour, baking soda, salt, cinnamon, and nutmeg and set aside.

In a stand mixer, beat the butter and sugars together on medium speed for 5 minutes until light and fluffy. Add in the vanilla, eggs, and sour cream and mix until combined, scraping the sides of the bowl as necessary.

Mix in the cooked oats and mix until just combined. Then fold in the flour mixture, mixing until just combined. It will be a very thick batter!

Spread batter into pans (around 600g each). Bake for 20-22 mins, until a toothpick comes out covered in a few moist crumbs. Cool in pans on a wire rack, then run a spatula around the edges to flip them out.

Next, make the buttercream. In a stand mixing bowl, beat the butter on medium speed until light and fluffy. Then mix in the powdered sugar on low speed. Once combined, increase the speed to medium and beat until the buttercream is light and fluffy, about 3-5 minutes. Mix in the heavy cream, vanilla extract, and vanilla bean paste.

Assemble by placing an oatmeal cake layer on a stand. Spread 1 cup of vanilla frosting on top. Add the next layer. Alternate cake and frosting layers, finishing with the top layer upside down for a flat surface.

Spread the rest of the frosting across the sides and top of the cake in a thin, even layer. Set the cake aside while you make the glaze.

Heat cream on the stove or microwave, then pour over the white chocolate chips, stirring to combine. Add the white food coloring for a less yellow tone (optional). Let it cool before pouring it over the cake to avoid melting the frosting.

Put the cake on a wire rack with a pan below. Pour the glaze in the center, spreading it to the edges so it falls off the sides. Let the glaze finish running off and set. Then decorate the top of the cake with crumbled oatmeal pie cookie crumbs and pieces.