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First, make the streusel topping. Mix the flour, brown sugar, cinnamon, and 1 tsp salt. Then cut in butter and mix just until small to medium clumps form. Mix in walnuts (optional) and refrigerate until needed.
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Preheat the oven to 350 degrees. Butter a 9" cake pan. Sift together flour, baking powder, baking soda, and 1/2 tsp salt.
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Start the cake batter; beat butter and sugar with a mixer 2 minutes on medium speed until fluffy. Add in eggs, one at a time, then vanilla. Add flour mixture in 3 batches. Alternating with the sour cream. Start with flour and end with flour. Add raisins (optional), Continue to beat in mixer until well combined.
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Spoon batter into cake pan and smoothen with a spatula. Remove streusel topping mix from the refrigerator and add to the top of batter, evenly.
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Bake until cake is golden brown, about 55 minutes. Check with a toothpick if the cake is done. Stick the toothpick into the center and it should come out clean.
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Put the pan on wire rack and let cool completely. Do not remove cake yet.
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After the cake is cool, remove the cake from the pan and prepare glaze.
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Mix confectioners sugar and coffee or any other flavored extract. Drizzle over cake and let rest for 5 minutes before serving.