- 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.