Thanks to Dorie Greenspan for this recipe.
1/2 cup flour
1/2 cup coarsely chopped walnuts
1/3 cup sugar
1 tablespoon grated orange zest
1/2 teaspoon instant espresso powder
1/2 teaspoon ground cardamom
4 tablespoons unsalted butter, cut into 8 pieces, at room temperature
2 cups flour
2 teaspoons baking powder
1/4 teaspoon salt
1 1/4 teaspoons ground cardamom
1 teaspoon instant espresso powder
2/3 cup sugar
2 tablespoons finely grated orange zest
8 tablespoons unsalted butter, melted and cooled
2 large eggs
1/2 cup milk
1/2 cup strong coffee, cooled
1 1/2 teaspoons pure vanilla
Center a rack in the oven and preheat the oven to 400 degrees F. Butter an 8-inch square baking pan, dust the inside with flour and tap out the excess.
To make the crumbs: Put all the ingredients except the butter in a bowl and toss them together with a spatula just to blend. Add the butter and, using your fingers or the spatula, mix everything together until you’ve got crumbs of different sizes. It’s nice to have a few big pieces, so don’t overdo it. Set the crumbs aside.
To make the cake: Whisk together the flour, baking powder, salt, cardamom, and espresso powder in a large bowl. Turn the dry ingredients out onto a sheet of wax paper, and put the sugar and zest in the bowl. Rub them together with your fingers until the sugar is moist and the fragrance of orange strong, then return the dry ingredients to the bowl and whisk to blend.
Put the remaining ingredients in another bowl and whisk them to blend. Pour the wet ingredients over the dry and stir – don’t beat – to mix. Stir only until you’ve got an evenly moistened batter. Scrape the batter into the prepared pan and top with a thick, even layer of the crumbs. Pat the crumbs ever so gently into the batter.
Bake for 30-35 minutes, or until the cake has risen (it will crown), the crumbs are golden and a thin knife inserted into the center comes out clean. Transfer to a rack to cool in the pan before serving warm or at room temperature.
You can unmold the cake if you want to, but you’ll lose some of the crumbs when you turn it over. Dorie prefers to cut the cake in the pan, taking care not to nick the surface of the pan with my knife. (This is a good job for a plastic or silicone pie server.)
Serving: Cut the cake into squares and serve warm or at room temperature.
Storing: This cake is best served the day it is made. It can be wrapped airtight and frozen for up to 2 months; once it defrosts, it benefits from a quick warm-up in a 350-degree-F oven.
I got the recipe here.