Start by toasting 3 slices of sourdough bread in a toaster or under the broiler until golden brown, about 3–5 minutes. Spread salted butter and raspberry conserve on each slice, then cool before processing into small flakes.

Melt 80g of unsalted butter in a saucepan over medium heat, stirring until golden brown and nutty, about 4–6 minutes. Remove from heat and let cool slightly.

Combine cold cubed unsalted butter, browned butter, 165g granulated sugar, and 60g muscovado sugar in a stand mixer. Beat until creamy, 3–4 minutes.

Add 1 large egg, 1 egg yolk, and 1 teaspoon vanilla extract to the butter mixture. Mix on medium speed until well combined, about 2 minutes.

In a separate bowl, whisk together 250g flour, 1/2 teaspoon baking soda, 1/4 teaspoon baking powder, and 1/4 teaspoon salt. Gradually add to wet ingredients on low speed until just combined.

Gently fold in 200g white chocolate chunks and 60g reserved toast flakes.

Spoon 120g of raspberry conserve over the dough, swirling gently to create a marbled effect.

Form balls of dough (80–90g each), roll in reserved toast flakes, and refrigerate for at least 1 hour.

Preheat oven to 190°C (374°F). Bake cookie dough balls for 9–11 minutes until edges are golden. Press reserved white chocolate into tops immediately after baking.

Let cookies cool for 5–10 minutes on the tray, then transfer to a wire rack.