Preheat oven to 350F (175C). Grease and flour a 9x13 inch baking pan.
In a large bowl, whisk together flour, sugar, baking soda, and salt.
In a separate bowl, combine plant-based milk, vegetable oil, apple cider vinegar, and vanilla extract.
Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix.
Gently fold in the strawberry puree and freeze-dried strawberry powder until evenly distributed.
Pour batter into the prepared pan and bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool completely in the pan before frosting.
Prepare the Vegan Buttercream: In a large bowl, beat vegan butter until smooth. Gradually add powdered sugar, alternating with plant-based milk, until the frosting reaches desired consistency. Stir in vanilla extract and salt.
Frost the cooled cake with the vegan buttercream frosting.
Cut the cake into individual serving sizes.
Freeze: Place the frosted cake slices on a baking sheet lined with parchment paper and freeze until solid, about 2-3 hours.
Freeze-Dry: Transfer the frozen cake slices to a freeze-dryer and process according to the manufacturer's instructions (typically 24-36 hours). Ensure that all moisture is removed.
Storage: Store freeze-dried cake slices in an airtight container at room temperature for extended shelf life.
Tips: For a richer flavor, use melted coconut oil instead of vegetable oil. To enhance the strawberry flavor, add a few drops of natural strawberry extract to the batter. When rehydrating, add a small amount of water or plant-based milk to the freeze-dried cake before consuming. Alternatively, pulverize and use it to make smoothies.