Step 1

Place a rack in middle of oven; preheat to 350°. Lightly grease bottom and sides of a 9"-diameter ovenproof skillet, preferably cast iron, with extra-virgin olive oil. Whisk 1 cup (100 g) blanched almond flour or almond meal, 2 Tbsp. cornstarch, and ½ tsp. baking powder in a medium bowl until well combined.

Step 2

Vigorously whisk 1 cup (packed; 200 g) light brown sugar, ½ cup (40 g) Dutch-process cocoa powder, 2 tsp. vanilla bean paste or vanilla extract, 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, ½ cup extra-virgin olive oil, and ¼ cup room-temperature water in a large bowl until combined and smooth. Add 2 large eggs and whisk to combine. Using a rubber spatula, gently fold in dry ingredients and 1 cup (170 g) semisweet chocolate chips (about 50% cacao) until just incorporated, scraping down sides and bottom of bowl to ensure no dry pockets of flour remain. Scrape batter into prepared skillet; smooth surface.

Step 3

Bake cake until puffy and set with no visible wet spots on top (cake is fudgy, so a tester isn’t of much use; err on the side of underbaking), 20–30 minutes. Let cool slightly.

Step 4

While the cake is baking, bring ¼ cup (packed; 50 g) light brown sugar, 2 Tbsp. Dutch-process cocoa powder, and ¾ cup water to a boil in a small saucepan over medium-high, whisking constantly. Remove from heat, add ½ cup (85 g) semisweet chocolate chips (about 50% cacao), and whisk until melted and smooth. Whisk in ⅓ cup (75 g) well-stirred tahini, 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, and 1 tsp. vanilla bean paste or vanilla extract until smooth (mixture will thicken once tahini is added). Let cool 10–15 minutes.

Step 5

To serve, scoop vanilla ice cream onto warm cake and drizzle with a few spoonfuls of fudge sauce. Sprinkle with a small pinch of flaky sea salt. Serve with remaining fudge sauce alongside.