Preheat your oven to 180°C (350°F). Grease your 9-inch cake pan and set aside.
Hull and blend the ripe strawberries until smooth to make about 1 cup of strawberry puree. Set aside.
In a mixing bowl, whisk together the sifted flour and baking powder until evenly combined.
In a large bowl, beat the softened butter and granulated sugar with a mixer until light, fluffy, and pale, about 3-4 minutes, with the mixer on medium speed.
Add eggs one at a time, beating well after each addition. Then mix in vanilla extract and the prepared strawberry puree, ensuring everything is incorporated smoothly.
Gradually add the dry ingredients in three parts, alternating with the milk, starting and ending with the flour mixture. Mix just until combined after each addition to keep the batter airy.
Pour the batter into the prepared pan, smoothing the top with a spatula. Tap the pan gently on the counter to release any air bubbles.
Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean and the top is golden. Once baked, remove from oven and let cool in the pan for 10 minutes.
Transfer the cake to a wire rack and allow it to cool completely, about an hour. This prevents the frosting from melting when you decorate.
To prepare the strawberry buttercream, beat the softened butter until creamy, then gradually add the sifted powdered sugar, heavy cream, and lemon juice. Beat until fluffy and smooth.
Spread a generous layer of the strawberry buttercream over the cooled cake, creating a rustic, textured finish. Let any excess frosting sit for a few minutes to settle.
Decorate with fresh strawberries if desired. Slice and serve to enjoy the charming, summery flavors of this rustic strawberry buttercream cake.
