1) Brew a very strong cup of coffee and cool it off in the fridge before continuing. You could do this the day before.
2) Finely chop your pecans or walnuts or pulse them a few times in a food processor. Then mix them with the cinnamon and sugar to finish the streusel. Set aside for later.
3) Combine all your dry ingredients for the cake and mix together.
4) Combine the cold strong coffee with the buttermilk and vanilla and whisk together. Set aside.
5) Preheat oven to 350 degrees and if you’re using a bundt pan, lightly butter it and dust it with flour so your cake will come out easily.
6) Using a stand mixer or hand mixer, beat together the sugar and soft butter until light and fluffy. About 5 minutes with a stand mixer or 10 minutes with a hand mixer.
7) Mix in one egg at a time, mixing on low after each egg.
8) Add your dry and wet ingredients to the batter in the following order, stirring after every step: 1/3 dry mix, 1/2 wet mix, 1/3 dry mix, the remaining wet mix, the remaining dry mix. Mix well and scrape down the sides of the bowl to make sure everything is well combined.
9) Pour half of your batter into your dish or bundt pan. Add all your streusel in an even layer. Then top with rest of your batter.
10) Bake at 350 degrees until a wooden skewer comes out cleanly, about an hour but it could vary based on your pan so just check it regularly.
11) Cool the cake for 10 minutes on a rack and then, if you used a bundt pan, invert it on a plate to carefully remove the cake. You can slide a knife around the sides of the pan to loosen the cake a bit.
12) Cool the cake completely.
13) If you’re using glaze, mix sifted powdered sugar and coffee until smooth, then drizzle over cake.
14) Let glaze harden for a few minutes then serve immediately.