For streusel topping: In a food processor add brown sugar, white sugar, cinnamon, flour, coffee powder, salt and cold butter. Blitz for 20-30 seconds until the butter is chopped and uniform in size like coarse sand. Place mixture in a bowl and add the coarsely chopped pecans; mix to combine. Divide mixture into two equal parts and set aside.
For cake batter: In a large bowl, whisk together flour, baking powder, bicarbonate soda and salt. Set aside.
Pre heat oven to 160ºC (fan forced). Grease and line the bottom and sides of a round 20cm springform pan with baking paper.
In the bowl of an electric mixer, cream together the butter and sugar until light and fluffy for about 3-4 minutes. Add eggs one at a time, beating in-between. Then add the vanilla and cooled coffee.
To this add 1/3 of the dry flour mix then 1/3 of the sour cream mixing on medium speed. Repeat another two times until all the flour and sour cream is incorporated into the batter.
Pour half the batter into the prepared pan. Top this with half the coffee streusel mixture and pat down gently. Add the remaining batter on top smoothing over gently. Cover the batter with the other half of the streusel mixture.
Bake in the oven for 60 minutes or until a skewer inserted into the middle comes out clean. When cool, dust with icing sugar, if desired.