|FOR THE CARAMEL, BOIL:|
|1||cup brown sugar|
|1||⁄2 cup golden syrup or corn syrup|
|3||⁄4 cup heavy cream, divided|
|1||⁄4 tsp. table salt|
|FOR THE CAKE, WHISK:|
|3||cups all-purpose flour|
|2||cups granulated sugar|
|1||⁄2 cup unsweetened cocoa powder|
|2||tsp. baking soda|
|1||tsp. table salt|
|2||cups hot water|
|3||⁄4 cup canola oil|
|2||Tbsp. distilled white vinegar|
|1||Tbsp. vanilla extract|
|1||tsp. instant espresso powder|
|1||can sweetened condensed milk (14 oz.)|
|FOR THE WHIPPED CREAM, BEAT:|
|3||cups heavy cream|
|1||⁄2 cup powdered sugar|
|1||cup chopped chocolate-covered toffee candy bar (such as Heath)|
Directions:For the caramel, boil brown sugar, golden syrup, 1⁄4 cup heavy cream, and 1⁄4 tsp. salt in a large saucepan over medium heat until mixture reaches 240° on a thermometer, 2–5 minutes. Whisk in remaining 1⁄2 cup heavy cream and transfer to a glass measuring cup with a pour spout; let cool to room temperature.
Preheat oven to 350°. Coat a 9×13-inch baking dish with nonstick spray.
For the cake, whisk together flour, granulated sugar, cocoa powder, baking soda, and 1 tsp. salt.
Combine hot water, oil, vinegar, vanilla, and espresso powder; whisk into dry mixture. Pour batter into prepared baking dish and bake until a toothpick inserted in the center comes out clean, about 25 minutes. Poke the cake all over with a fork while still hot.
Spread sweetened condensed milk evenly over the cake and allow to soak in. Spread caramel evenly over the cake. Allow cake to cool to room temperature, then cover and chill until cold, at least 2 hours or overnight.
For the whipped cream, beat 3 cups heavy cream to nearly stiff peaks; add powdered sugar, and beat to combine. Spread whipped cream over chilled cake, then sprinkle toffee bar over the top.