Heat your oven to 160C fan/180C.
Line a cake tray with baking paper - I used a 25X35 tray.
Whisk together the butter, sugar and vanilla together for a few minutes. Don't over mix which is particularly easy to do when using dairy free butter.
Add the eggs into the bowl and mix well between each egg.
Next add the oat milk, baking powder and flour. Beat 'til you have a smooth batter.
Pour the cake mixture into your baking tray and pop it into the oven for 30-40 minutes. Keep an eye on the cake because all ovens can vary.
Remove the cake from the oven once a skewer (or knife) comes out clean.
Remove the cake from the baking tin and leave it to fully cool on a wire cooling rack.
Once the cake is cool it's time to make the icing, the best part! Firstly sift the icing sugar into a mixing bowl.
Then, very slowly add a little milk (or water) and mix. Continue doing this 'til your icing is at your desired consistency. I like mine to be lovely and thick.
Spread the icing over your cake (do make sure it's cool) and then cover it with sprinkles.
Let it set for 30 minutes and then slice and serve up with a cuppa tea.