Instructions

• Zest enough blood oranges to get 1 teaspoon of very finely grated zest; set zest aside. Juice blood oranges and strain the juice through a fine-mesh sieve to remove pith and flesh. You need 1 cup (240 g) freshly squeezed, strained juice.
• Pour the 1 cup (240 g) strained orange juice into a medium saucepan and simmer over medium-high heat, stirring occasionally, until reduced by half (about 10–15 minutes). You should have about 1/2 cup of reduced juice. Remove from heat and stir in 1/4 teaspoon citric acid (or 2 tablespoons lemon juice) until dissolved. You can refrigerate this reduced juice if making ahead.
• Set up a double boiler: put 1–2 inches of water in a saucepan and bring to a gentle simmer. Use a medium heatproof bowl that will sit above the water without touching it.
• In the heatproof bowl, whisk together 2 large eggs, 4 large egg yolks, 1/2 cup (100 g) granulated sugar, and the 1 teaspoon blood orange zest until smooth. Whisk in 1/2 cup of the reduced orange juice.
• Place the bowl over the simmering water (water should be at a gentle simmer so it does not touch the bowl). Cook, whisking constantly or very regularly, and adjust the heat so the water remains a gentle simmer. Continue until the curd thickens and registers about 165°F (74°C) on an instant-read thermometer or coats the back of a spoon. Remove the bowl from the heat.
• If the curd has any cooked egg bits, press it through a fine-mesh sieve into a clean bowl to remove them. Set the curd aside to cool slightly while you make the brownie layer (it should be cool enough to handle but still pourable when you use it).
• Preheat the oven to 350°F (175°C). Lightly butter an 8-by-8-inch square baking pan, line it with parchment so the parchment overhangs two sides, and butter the parchment lightly to help it stay in place.
• Make the brownie batter: in a small saucepan over medium heat, melt 1/2 cup (113 g) unsalted butter. When melted and beginning to bubble, remove from heat. Stir in 3/4 cup (150 g) granulated sugar until smooth and paste-like.
• Whisk in 1 tablespoon (14 g) vegetable oil. Add 1 large egg and 1 large egg yolk and whisk vigorously for about 1 minute until combined and slightly aerated. Whisk in 1 teaspoon vanilla extract.
• Sift in 1/2 cup (50 g) Dutch-process cocoa powder. Add 1/3 cup (42 g) all-purpose flour and 1/4 teaspoon fine sea salt. Fold the dry ingredients into the wet until just incorporated; do not overmix.
• Transfer the thick batter to the prepared pan by dropping dollops around the pan, then use a thin offset spatula to spread the batter into an even layer.
• Bake the brownie base for 15–17 minutes, until the top appears uniformly set but the interior is still quite gooey.
• Remove the pan from the oven. Pour the warmed orange curd over the partially baked brownie layer and gently spread into an even layer, taking care not to disturb the brownie too much.
• Return the pan to the oven and bake 5–7 minutes more, until the curd layer appears evenly set.
• Remove the pan from the oven and place it on a wire rack. Cool at room temperature for about 1 hour, then refrigerate for at least 1 hour (or overnight) until fully set.
• Use the parchment overhang to lift the brownie slab from the pan. Cut into 16 squares. For the cleanest cuts, warm a large chef’s knife under hot water, dry it, wipe the blade with a little oil or butter, and re-warm/re-oil between cuts as needed.
• Store brownies refrigerated in an airtight container for up to 3 days.