Preheat oven to 350 degrees and grease a 9x13 inch baking pan.
In a medium bowl combine oats and hot water, stir, let soak while you prepare next steps.
In a medium bowl whisk together flour, baking soda, baking powder, salt, cinnamon, and nuts (if including).
In a large bowl cream together the butter, brown sugar, and sugar for 2-3 minutes. Mix in the eggs and vanilla.
Mix in oatmeal, then mix in dry ingredients just until combined.
Spread mixture evenly in prepared pan. Bake for 35 minutes until set and a toothpick inserted in the middle comes out with no wet batter. Allow cake to cool for 15-20 minutes, meanwhile prepare the vanilla sauce.
In a thick-bottom medium sauce pan (do not use stainless steel) over medium heat, combine butter, sugar, heavy cream, vanilla, and salt. Stir continuously for about 5 minutes until sauce is thick enough to coat the back of a spoon.
Cut cake into squares, drizzle vanilla sauce over the top, and serve.