Pre-heat oven to 180°C/356°F. Line a 9×13 cake pan.
The cake: Start by making the buttermilk by combining oat milk with apple cider vinegar. Set aside for 5 minutes. In another bowl, mix together light brown sugar with the melted butter. Mix in vanilla extract, the buttermilk and grated carrots. In another bowl, combine the flour, baking soda, baking powder, ground cinnamon and salt. Set aside.
Maple caramel: Add maple syrup, dark brown sugar, butter and vanilla extract into a saucepan. Heat over medium heat, once the butter has melted, bring to a boil and boil for 3-4 minutes or until it becomes thicker.
Baking the cake: Combine the wet and dry together, and pour into the pre-lined baking sheet. Smooth out into an even layer. Drizzle 3 tbsp of the maple caramel, and quickly swirl together. Bake for 30-40 minutes or until a toothpick comes out clean when inserted.
Cream cheese frosting with caramel: Beat together softened room temp butter with the cream cheese. Once smooth, add in small amounts of the icing sugar at a time, and mix until combined. The maple caramel will stiffen up, so to loosen it up add 1 tbsp of oat milk to it and bring to a gentle boil until everything is mixed and runnier. Set aside.
Final touches: Once the cake is baked, allow to cool for 20 minutes in the cake pan, then remove to cool completely before frosting. Dollop the vegan cream cheese frosting all over the cake, spread and create swirls. Drizzle over the maple caramel, and swirl together. Enjoy!!