Begin your culinary adventure by preparing the champagne cake base. In a large mixing bowl, whip together the eggs and granulated sugar using an electric mixer on medium speed until the mixture becomes light and fluffy, which should take about 5-7 minutes. In a separate bowl, whisk together the sour cream, vegetable oil, milk, vanilla extract, and champagne until well blended. In another bowl, combine the all-purpose flour, baking powder, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.

Now it's time to bake! Preheat your oven to 350°F (175°C). Next, evenly divide the batter between two 6-inch cake pans that have been greased and lined with parchment paper. Bake the cakes for approximately 35-40 minutes until they are golden and a toothpick inserted into the center comes out clean. Once baked, transfer them to a wire rack and allow them to cool in the pans for about 10 minutes, then turn them out onto the rack to cool completely.

While the cake layers cool, focus on making the strawberry frosting. Start by combining egg whites and sugar in a heatproof bowl over a simmering pot of water (double boiler). Whisk continually until the mixture is warm to touch and the sugar is completely dissolved, about 4-5 minutes. Next, transfer the bowl to your mixer, and beat on high speed until it cools down to room temperature and forms stiff peaks, which typically takes around 8-10 minutes.

With the meringue ready, switch to the paddle attachment and add the cold butter, one cube at a time, mixing on medium speed. Continue to beat the mixture until it becomes smooth and creamy, which should take about 5 minutes. Then, gently fold in the fresh strawberry puree and any optional food coloring until fully incorporated.

Now that both your cake layers and frosting are ready, it's time to assemble your masterpiece! Carefully slice each cake layer in half horizontally, creating a total of four layers. Place the first layer on a serving plate and spread a generous layer of strawberry buttercream on top. Stack the second layer, repeating the frosting process until all layers are assembled. After stacking, apply a thin crumb coat of frosting to the top and sides of the cake; this helps to seal in any crumbs.

To ensure your cake is beautifully finished, refrigerate it for about 30 minutes to let the crumb coat set. Once set, generously frost the top and sides of the cake with the remaining strawberry buttercream, smoothing it out for a polished look. For the final touch, feel free to garnish with fresh strawberries, edible flowers, or a sprinkle of pomegranate seeds. Your stunning Strawberry Champagne Cake is now ready to be the centerpiece of your celebration!