Step 1

Preheat the oven to 350°F with a rack in the center. Grease an 8" round pan or a 9" tart pan with a removable bottom, line the bottom with a parchment round, and lightly grease. (An 8" round pan will give you a slightly taller, fudgier cake.)

Step 2

, To make the date cake: Place the dates and baking soda in a small glass bowl or liquid measuring cup. Cover with boiling water and set aside until the dates are very soft, about 10 minutes. (The baking soda helps soften the dates and makes for a smoother batter.)

Step 3

, Meanwhile, in a medium bowl, whisk together the flour, cocoa, salt, baking powder, and espresso powder.

Step 4

, When the dates are nearly done soaking, in a large bowl, vigorously whisk together the brown sugar, egg, egg yolk, and vanilla until the sugar is completely dissolved and the mixture has lightened in color and become foamy, about 2 minutes. While whisking, slowly drizzle in the oil until the mixture is emulsified, creamy, and shiny.

Step 5

, Switch to a flexible spatula and gently stir in the flour mixture until nearly incorporated. Add the chopped chocolate to the bowl, then drain the dates and add them on top of the chocolate. Stir to incorporate the dates and chocolate into the batter while smashing some of the dates apart; you will have a thick, fudgy, shiny batter.

Step 6

, Transfer the batter to the prepared pan and spread into an even layer. (A small offset spatula is a helpful tool here.)

Step 7

, Bake the date cake for 18 to 22 minutes, until the top feels set and a toothpick or paring knife inserted into the center comes out mostly clean but with some streaks of melted chocolate. The internal temperature should be at least 190°F when a digital thermometer is inserted into the cake about 1" from the edge.

Step 8

, Transfer the date cake to a wire rack to cool slightly. When cool enough to handle, remove the cake from pan and set on the wire rack to cool completely.

Step 9

, To make the whipped cream: In a medium bowl or the bowl of a stand mixer, use a whisk or the flat beater attachment to whip the cream, yogurt, and sugar, until soft peaks form.

Step 10

, To make the date butterscotch: Place the dates in a small heatproof bowl and cover with boiling water. Set aside.

Step 11

, In a small, heavy-bottomed saucepan, combine the butter, brown sugar, and salt. Bring the mixture to a boil over medium heat and cook, whisking frequently, for 1 minute, until the mixture is thick and foamy and coats the back of a spoon or spatula.

Step 12

, Drain the dates, transfer them to a food processor, and add the butter/brown sugar mixture. Add 2 tablespoons of the hot soaking water and process until smooth. Add more hot water, by the teaspoon, until your butterscotch is thin enough to drizzle. Taste and season with more salt, if necessary.

Step 13

, Serve slices of the date cake at room temperature with whipped cream and warm date butterscotch.

Step 14

, Storage information: Store the date cake, well-wrapped at room temperature, for up to 4 days. Store date butterscotch in an airtight container in the refrigerator for up to 1 week. Reheat in the microwave on low power to loosen. Store whipped cream in the refrigerator for up to 2 days (the yogurt helps to stabilize it); re-whisk as needed.