Heat 1 tablespoon of oil and 1 tablespoon of butter in a heavy based pan. Add the shallots and sauté until softened but not coloured. Add the oatmeal and stir for a minute or two to lightly toast the grains.
Add the stock and bring to the boil. Once boiling, lower the heat and simmer for about 20 minutes until the oats are tender but still retain some bite. Season with the celery salt and nutmeg. Taste to check if you need anymore salt - this will depend on how salty your stock is - and season with pepper.
Whilst the oats are cooking, sauté the brussels sprouts in the remaining tablespoon of butter, until softened and lightly browned, about 5 minutes. Towards the end of cooking, stir in the grated garlic clove. Season with salt.
Pour the oatmeal into bowls and top with the brussels sprouts. Top with a fried egg and bacon, if using.
This doesn't make a huge amount of porridge, so feel free to increase the quantities if you like. It's pretty filling though, so the quantities listed really do make a nice bowlful, especially with a rich, yolky egg on top.