Center a rack in the oven and preheat it to 325 degrees F. Coat the inside of an 8-x-8-inch baking pan, one with at least 2-inch- high sides, with baker’s spray (it’s better than butter and flour for this cake) and then line the bottom and sides of the pan with two pieces of parchment, crisscrossing them so that all four sides are covered with paper; spray the parchment.

To make the nut layer: Put the sugar and butter in a saucepan over medium heat and cook, stirring, until the sugar dissolves, the butter melts and the mixture boils. Cook, stirring, for a minute or two, then add the cream, salt and cinnamon, bring back to a boil and cook and stir for another 2 minutes. Add the nuts and stir until they are coated with the caramel.

Turn the mixture out into the baking pan and use a flexible spatula to spread it into the corners and to even the layer. Set aside.

To make the cake: Put the butter and chocolate in a small saucepan and set it over very low heat. You want to melt the butter and chocolate slowly so that they blend beautifully and don’t get so hot that they separate. (If your stovetop doesn’t have a very low setting, melt the butter and chocolate in a heatproof bowl set over a pan of gently simmering water—the bottom of the bowl should not touch the water—or do this in a microwave.)

Whisk the flour, espresso powder, baking powder, salt and cinnamon together.

Put the sugar in a large bowl, drop in the eggs and immediately start whisking, then continue to whisk energetically for a couple of minutes. Pour in the melted chocolate-butter—it might still be a little warm, and that’s fine—and whisk to incorporate completely. Add the dry ingredients and, continuing with the whisk or trading it for a flexible spatula, mix them in until there’s no trace of flour. Scrape the batter into the pan and smooth the top.

Bake for 34 to 37 minutes, or until the top looks dry, the cake starts to pull away from the sides of the pan and, most important, a tester poked into the center of the cake comes out clean or with a few dry crumbs. Transfer the pan to a rack and let it sit for 10 minutes.

Very carefully—the caramel will be super hot—turn the cake out onto another rack and peel away the parchment. If a few nuts and some caramel have stuck to the paper, use a table knife to scrape them off and onto the cake. Let the cake cool to room temperature. It’s tempting to eat the cake when it’s only just warm—and I wouldn’t stop you—but the texture of both the nuts and the cake is better after a few hours. In fact, I think this cake really comes into its own the next day.