Caramel-Nut Chocolate Upside-Down Cake

Ingredients

• ½ cup (100 g) light brown sugar
• 3 tablespoons (42 g) unsalted butter
• ¼ cup (60 ml) heavy cream
• ½ teaspoon fine sea salt
• ¼ teaspoon ground cinnamon
• About 1½ cups (170 g) pecans or walnuts, coarsely chopped and at room temperature
• 12 tablespoons (170 g) unsalted butter, cut into chunks
• 6 ounces (170 g) semisweet or bittersweet chocolate, coarsely chopped
• ¾ cup (102 g) all-purpose flour
• 1 teaspoon instant espresso powder
• ½ teaspoon baking powder
• ½ teaspoon fine sea salt
• ¼ teaspoon ground cinnamon
• ⅔ cup (134 g) granulated sugar
• 2 large eggs, at room temperature

Instructions

1. Center a rack in the oven and preheat to 325°F (165°C). Coat an 8-inch square baking pan with at least 2-inch-high sides with baker’s spray. Line the bottom and all four sides with two crisscrossed sheets of parchment, then spray the paper.
2. Make the nut layer: Put the brown sugar and 3 tablespoons butter in a saucepan over medium heat. Cook, stirring, until the sugar dissolves, the butter melts, and the mixture bubbles.
3. Cook for 1 to 2 minutes, then stir in the cream, salt, and cinnamon. Return to a boil and cook, stirring, for 2 minutes. Add the nuts and stir until every piece is coated with caramel.
4. Spread the caramel-nut mixture evenly over the bottom of the prepared pan, pushing it into the corners. Set aside while you make the cake batter.
5. Melt the 12 tablespoons butter and chopped chocolate together in a heatproof bowl over barely simmering water, or in short microwave bursts. Stir until smooth and glossy; let cool for about 5 minutes.
6. Whisk the flour, espresso powder, baking powder, salt, and cinnamon together in a small bowl.
7. In a large bowl, whisk the granulated sugar and eggs vigorously for about 2 minutes, until slightly thickened and pale. Slowly whisk in the warm chocolate mixture until smooth.
8. Fold in the dry ingredients with a flexible spatula just until no flour streaks remain. Gently spread the batter over the caramel-nut layer without disturbing it.
9. Bake for 32 to 38 minutes, until the top is set and a tester inserted in the center comes out with a few moist crumbs. Cool in the pan for 10 minutes, then run a thin knife around the edges and invert the cake onto a serving plate while still warm. Peel away the parchment and let cool before cutting into 9 to 12 squares.