Preheat the oven to 350°F and spray a 9×13-inch baking pan with nonstick cooking spray.

In a large bowl, whisk together 1 box French vanilla cake mix, 1 cup whole milk, 3 large eggs, and 1/3 cup oil until smooth. Pour the batter into the prepared baking pan.

Bake for about 25 minutes, or according to the package directions, until the cake is lightly golden and a toothpick inserted in the center comes out clean.

While the cake is still warm, use the handle of a wooden spoon to poke holes across the cake, spacing them about 1–1½ inches apart. Let the cake cool completely.

If using, spoon or brush 2–3 tablespoons strong brewed coffee (cooled) evenly over the cake, allowing it to soak into the holes.

In a medium bowl, whisk together 1 (3.4-ounce) box instant vanilla pudding mix and 2 cups whole milk until smooth and slightly thickened. Spread the pudding evenly over the cooled cake, gently pressing it into the holes. Sprinkle 2 teaspoons finely ground espresso powder evenly over the pudding layer. Refrigerate for 10–15 minutes to set.

In a large bowl, beat 1½ cups heavy cream, 1/2 cup powdered sugar, and 1/2 cup sour cream until stiff peaks form, about 3–5 minutes. Spread the whipped topping evenly over the cake.

Dust the top with 3 teaspoons unsweetened cocoa powder using a fine-mesh sieve. Refrigerate for at least 1 hour before slicing. Serve chilled.