Preheat your oven to 350°F (175°C). Lightly grease and flour a 9x13 inch baking pan, or line it with parchment paper for effortless removal. This crucial step ensures your cake won't stick and releases cleanly after baking.

In a large mixing bowl, beat the softened unsalted butter with an electric mixer until it's light and creamy, about 1-2 minutes. Gradually add the granulated sugar and continue beating on medium-high speed until the mixture is visibly pale and fluffy, another 2-3 minutes. This aeration process creates a wonderfully tender cake crumb.

Add the three egg whites and one whole egg, one at a time, beating well after each addition until fully incorporated and the mixture appears light and airy. Next, mix in the room temperature whole milk, strawberry gelatin powder, and pure vanilla extract until just combined. Remember to scrape down the sides of the bowl to ensure everything is mixed evenly.

In a separate medium bowl, whisk together the sifted all-purpose flour, baking powder, baking soda, and fine sea salt. Sifting the flour is key; it prevents lumps and ensures an even distribution of the leavening agents for a uniform, perfect rise.

Gradually add the dry ingredient mixture to the wet mixture, beating on low speed until just combined. Be very careful not to overmix the batter; excessive mixing can overdevelop the gluten, resulting in a tough cake. Mix only until no streaks of flour remain.

Pour the prepared cake batter evenly into your greased and floured baking pan. Bake for 20-25 minutes, or until a wooden skewer or toothpick inserted into the center of the cake comes out completely clean. The cake's top should be lightly golden and spring back when gently touched.

Allow the cake to cool in the pan on a wire rack for at least 15-20 minutes before carefully inverting it onto the rack to cool completely. A fully cooled cake is absolutely essential before applying frosting; otherwise, the buttercream will melt and slide off.

For the buttercream frosting, in a large mixing bowl, beat the softened unsalted butter on medium speed with an electric mixer until it's wonderfully creamy and smooth. Pour in the heavy cream, pure vanilla extract, and a pinch of fine sea salt, beating until all ingredients are fully incorporated.

Gradually add the sifted confectioners' sugar to the butter mixture, starting on low speed to prevent a 'sugar cloud,' then increasing to medium-high speed. Beat for 3-5 minutes until the frosting is visibly light, fluffy, and easily spreadable. The extended beating incorporates air, making it incredibly airy.

Prepare the irresistible crunch topping by placing the Golden sandwich cookies (without their cream filling) and lightly crushed freeze-dried strawberries into a food processor. Pulse until fine crumbs form. Alternatively, place them in a sturdy Ziploc bag and crush them thoroughly with a rolling pin. Transfer the crumbs to a bowl and pour in the melted and *cooled* unsalted butter. Toss gently until the crumbs are evenly coated. Ensuring the butter is cool is vital to prevent the crunch from becoming soggy later.

Once the cake is completely cool, spread an even, generous layer of the fluffy vanilla buttercream frosting over the top. Then, generously sprinkle the prepared strawberry crunch topping evenly over the frosting. For the best slicing and serving experience, chill the cake for at least 30 minutes to allow the frosting to set before cutting. Enjoy your amazing Strawberry Crunch Cake!