Preheat oven to 350°F (175°C). Grease and line a square baking pan with parchment paper.

Beat butter and sugar until pale and fluffy.

Add eggs one at a time, beating well after each addition.

Mix in lemon zest and lemon juice.

In a separate bowl, whisk together cake flour, baking powder, and salt.

Add dry ingredients to the butter mixture, alternating with milk, on low speed until smooth. Do not overmix.

Pour batter into the prepared pan and spread evenly.

Scatter mashed raspberries over the batter and gently press some in.

Bake 40–45 minutes, until a toothpick comes out clean.

Cool before slicing. Serve plain or topped with powdered sugar, whipped cream, or extra raspberries.