• Preheat the oven to 350F and line an 8x8 inch square pan with parchment paper or grease the pan lightly. Set aside for later.

Make the vanilla cake batter:

• Add the oat milk and apple cider vinegar to a large mixing bowl and whisk together. Let sit for 2-3 minutes to curdle and create the “vegan buttermilk”.
• Next, add the sugar, melted vegan butter, and vanilla to the bowl and whisk together. Then, add in the dry ingredients starting with the all-purpose flour and then add the baking powder, salt, and baking soda on top.
• Mix into a thick batter. I recommend starting with a whisk and then switching to a spatula so the batter does not get over-mixed.

Make the cinnamon sugar filling:

• Add the brown sugar, softened vegan butter, and cinnamon to a bowl and mash together until a smooth paste forms. You can also use a food processor to mix together.

Assemble & bake the cake:

• Pour the vanilla cake batter into the parchment-lined pan and use a spatula to spread it out evenly. Then, drop spoonfuls of the cinnamon sugar filling on top of the batter.
• Use a knife to swirl the top layer of cinnamon sugar into the vanilla cake batter to create a marble effect.
• Then, add the cake to the oven and bake for 30-32 minutes.

Make the vanilla icing & serve:

• Immediately after removing the cake from the oven, make the glaze. Whisk together the powdered sugar, oat milk, and vanilla bean paste until a thick glaze forms.
• While the cake is still warm, pour the glaze over the cake so it seeps in for that classic cinnamon roll flavor.
• Transfer the cake to a wire rack to finish cooling. Once cooled, slice into 9 squares, serve, & enjoy!