Coffee cake with streusel

Whisk the streusel flour, dark brown sugar and cinnamon together until homogenous with no large lumps.

Whisk in the turbinado sugar and quarter teaspoon of baking powder.

Pour in 12 tablespoons of melted unsalted butter and combine with two forks or your hands until crumbly; cover and set aside.

Whisk the cake flour, baking powder, baking soda and kosher salt together.

Cream 6.5 oz granulated sugar with one stick of room temperature unsalted butter, on low then medium high for about three minutes, until light, pale and fluffy.

Scrape the bowl and beat in the eggs, ideally one at a time for about 30 seconds each.

Beat in the vanilla extract and a cup of room temperature sour cream on medium for one to two minutes, scraping halfway.

Sift in the dry ingredients and mix on medium low for 30 seconds, scrape the bowl, then mix another 30 seconds until smooth, taking care not to overmix.

Spray a loaf pan, line it with parchment and grease the parchment too.

Lay about half the batter in the pan, sprinkle in about a third of the streusel, press it gently in and push it away from the edges with a rubber spatula so it is encased.

Top with the remaining batter, spread evenly and press into the corners so the streusel layer is sealed in.

Apply the top crumb layer of streusel and press it down lightly.

Bake at 350F with the rack at its lowest point for 50 to 60 minutes, until risen, deeply brown, and a tester comes out with only a few moist crumbs.

Cool in the pan 45 minutes, lift out by the parchment, then cool completely on a wire rack up to an hour and a half.

While still slightly warm, dust heavily with powdered sugar so it adheres to the crumbs.

Slice with a long bread knife.