Prep the pan: Heat the oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment, leaving overhang for easy lifting. Lightly grease the parchment.

Melt the butter: Melt the butter and let it cool for 5–7 minutes until warm but not hot. This helps keep the blondies thick and fudgy.

Mix sugars and butter: In a large bowl, whisk the melted butter with the brown sugar and granulated sugar until glossy and well combined, about 45 seconds.

Add eggs and vanilla: Whisk in the eggs, egg yolk, and vanilla (and lemon zest if using) until the mixture thickens slightly and looks smooth.

Combine dry ingredients: In a separate bowl, whisk the flour, baking powder, and salt. Add to the wet mixture and fold gently with a spatula until just combined. Do not overmix.

Stir in the chocolate: Fold in the white chocolate, reserving a small handful for the top.

Add raspberries: Gently fold in the raspberries with 2–3 light strokes. It’s fine if some streak and break; avoid overmixing so the batter doesn’t turn purple.

Spread and top: Scrape the batter into the prepared pan and smooth the top. Sprinkle the reserved white chocolate over the surface.

Bake: Bake for 28–34 minutes, until the edges are golden, the top is set, and a toothpick inserted near the center comes out with a few moist crumbs (not wet batter).

Cool and slice: Let the blondies cool in the pan on a rack for at least 1 hour. Lift out using the parchment and cut into squares. For the cleanest cuts, chill for 30 minutes first.