For the cake: In a medium bowl, combine the currants, oats and stout; cover and set aside for 2 hours.
For the streusel: In the bowl of an electric mixer, mix granulated sugar, brown sugar, flour, caraway seeds and salt until combined. Add butter; mix until mixture resembles coarse cornmeal. Add nuts; mix until mixture begins to clump together. Transfer mixture to refrigerator until ready to use.
Preheat the oven to 350 degrees.
For the cake: In an electric mixer fitted with paddle attachment, beat the butter until smooth, about 1 minute. Add the granulated sugar, brown sugar and salt in a slow, steady stream. Mix on low speed until combined, scraping down the sides of the bowl once. Beat the butter and sugars until light and fluffy, 4 to 5 minutes. With the mixer on medium-low, add the eggs in a slow, steady stream. Scrape down the sides of the bowl often. Strain the currants and oats from the stout, reserving the stout, and transfer the oats and currants to a small bowl. With the mixer on low, add the flour in 3 batches and the stout in 2, beginning and ending with the flour. Mix until just moistened. Fold in the currants and oats.
Transfer the batter to a 10-inch buttered springform pan and sprinkle with the streusel topping. Bake the cake, rotating the pan once, until it is golden brown and springs back when touched, 25 to 30 minutes. Let cool completely on a wire rack.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.