Simmer the strawberry puree in a small saucepan over medium-low heat for 10-15 minutes until reduced to 1/4 cup. Allow to cool completely.
Preheat the oven to 350°F (175°C) and grease one 6-inch round cake pan with oil or parchment paper.
Combine the almond milk and apple cider vinegar in a small cup and let stand for 5 minutes to create vegan buttermilk.
In a medium mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
Add the cooled strawberry reduction, oil, vanilla extract, and buttermilk mixture to the dry ingredients.
Whisk the batter until just combined, ensuring no large flour pockets remain, but do not overmix.
Pour the batter into the prepared cake pan and bake for 28 to 32 minutes, or until a skewer inserted in the center comes out clean.
Cool the cake in the pan for 10 minutes, then invert onto a wire rack to cool completely before frosting.