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.

Preheat the oven to 350 degrees. Butter a 9" cake pan. Sift together flour, baking powder, baking soda, and 1/2 tsp salt.

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.

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.

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.

Put the pan on wire rack and let cool completely. Do not remove cake yet.

After the cake is cool, remove the cake from the pan and prepare glaze.

Mix confectioners sugar and coffee or any other flavored extract. Drizzle over cake and let rest for 5 minutes before serving.