Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper leaving a 2-inch overhang along each side.
Combine white chocolate and butter in a heatproof bowl and place it over a saucepan with barely simmering water. Stir until completely melted and smooth. Or melt in the microwave at 50% power in short bursts with frequent stirring.
Combine eggs, sugar, lemon zest and salt in a large bowl and whisk or beat with an electric hand mixer until pale and thick. Mix in vanilla. Mix in warm melted white chocolate mixture. Add 1 cup of flour and fold it in gently. Just before all of the flour is incorporated, fold in the chocolate chips. Toss raspberries with 1 tablespoon of flour and gently fold them into the batter.
Spread the rest evenly into prepared pan. Bake for 24-28 minutes until the top is shiny and crackly. Transfer to a wire rack and let cool completely in the pan before slicing into squares.