Prepare the Batter
Preheat the oven to 350°F (175°C) and grease a 9x13-inch baking dish.
In a small bowl, mix almond milk and vinegar; set aside to curdle (your vegan buttermilk).
In a large bowl, combine flour, sugar, baking powder, soda, salt, cinnamon, and nutmeg.
Add the oil, vanilla, and buttermilk to the dry ingredients, mixing until smooth.
Make the Streusel
In another bowl, combine flour, brown sugar, and cinnamon.
Add cold vegan butter cubes and mix with your hands until crumbly.
Assemble and Bake
Pour the batter into the prepared dish, spreading evenly.
Sprinkle the streusel generously over the batter.
Bake for 35 minutes, or until a toothpick inserted in the center comes out clean.
Let cool for 10 minutes before slicing.