Whisk together your brown sugar and cinnamon. Set aside.
Prepare Streusel
In a medium jug or bowl, whisk together the sugar, salt, flour and cinnamon
Melt your butter in a small saucepan or in the microwave. Pour the melted butter over your dry ingredients and use a whisk to get the dry ingredients evenly moistened. Fold in your chopped pecans. Make sure there are no dry spots left, as these may sink in the cake batter. Place the jug or bowl in the fridge to firm up while you make the cake.
Make cake
Preheat oven to 350°F/175°C. Grease a 8x8" pan with butter and parchment paper. Have the paper overhang the sides of the pan, this will make it easier to remove the coffee cake when it has cooled.
In a stand mixer, beat the butter, salt, sugars, cardamom, baking powder and vanilla until smooth with a paddle attachment. Add the eggs one at a time, beating well after each addition.
Add ⅓ of flour to the stand mixer bowl, beating until well combined. Add ⅓ of the the sour cream. Repeat this once more, then end with the final third of flour. Make sure there are no flour pockets but don't overmix the batter.
Pour half of the batter into the prepared pan. Sprinkle the filling on the batter, then pour the remaining batter on top. Use an offset spatula to evenly cover the filling. Sprinkle the streusel topping over the batter.
Bake until golden brown, 30-35 minutes. A toothpick inserted will come out clean
Notes
My recipes have been developed and tested in metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way. I have provided a conversion to US cups but please note that I haven’t tested the recipe with this method. Just click on ‘US customary’ above the ingredients.Room Temperature: I make sure that all of my ingredients are at room temperature before I start the recipe, so pull out all of the ingredients about 2 hours before you start baking. Salt: If you don't have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt.Butter: I use European style butter, like Kerry Gold, in my recipes.Sour Cream: you can substitute sour cream for full fat yogurt. I don't recommend using any low fat or non fat products as it will change the texture and taste. Storage: Keep the cake wrapped up tightly or in an airtight container. It will last 3 days at room temperature and up to a week in the fridge.