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Slice of buttermilk blueberry coffee cake with juicy blueberries and brown sugar cinnamon streusel

Buttermilk Blueberry Coffee Cake with a Tender Crumb

A 9-inch square buttermilk blueberry coffee cake with a soft, fine crumb, juicy blueberries, and a separate layer of crisp brown sugar cinnamon streusel.
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Prep Time 25 minutes
Cook Time 50 minutes
Cooling 1 hour 30 minutes
Total Time 2 hours 45 minutes
Servings: 12 slices
Course: Dessert
Cuisine: American
Calories: 351
Ingredients Equipment Method Notes

Ingredients
  

  • 120 g all-purpose flour 1 cup, for the streusel
  • 100 g light brown sugar 1/2 cup, firmly packed
  • 1 1/2 tsp ground cinnamon for the streusel
  • 1/4 tsp fine sea salt for the streusel
  • 85 g unsalted butter 6 tbsp, melted and cooled for 5 minutes
  • 250 g all-purpose flour 2 cups, spooned and leveled if not weighed
  • 2 tsp baking powder level
  • 1/2 tsp baking soda level
  • 1/2 tsp fine sea salt for the cake batter
  • 113 g unsalted butter 1/2 cup, softened to about 18 to 21°C
  • 180 g granulated sugar about 3/4 cup plus 2 tbsp
  • 2 large eggs at room temperature
  • 2 tsp pure vanilla extract for the cake batter
  • 180 ml cultured buttermilk 3/4 cup, shaken and at room temperature
  • 250 g blueberries about 1 1/2 cups, fresh or frozen and not thawed

Equipment

  • 9-inch square light-colored metal baking pan
  • Parchment paper
  • Digital kitchen scale or dry and liquid measuring cups
  • Stand mixer with paddle attachment or electric hand mixer
  • Two medium mixing bowls
  • Large mixing bowl if using a hand mixer
  • Whisk
  • Flexible silicone spatula
  • Small offset spatula or spoon
  • Wire cooling rack
  • Wooden skewer or thin paring knife

Method
 

  1. Position a rack in the center of the oven and heat it to 350°F (177°C). Lightly grease a 9-inch square metal pan, then line the bottom and two opposite sides with parchment to form a sling. Set the pan aside. Bring the batter butter, eggs, and buttermilk to room temperature so the mixture emulsifies smoothly. If using fresh blueberries, rinse them only if needed and dry them thoroughly before measuring.
  2. In a medium bowl, whisk the streusel flour, brown sugar, cinnamon, and salt until no compact sugar lumps remain. Pour in the melted butter and stir with a fork until all dry patches disappear. Squeeze portions between your fingers to create clusters ranging from pea-sized crumbs to pieces about 1/2 inch wide. Refrigerate the bowl while preparing the batter so the butter firms and the topping stays distinct during baking.
  3. In a clean medium bowl, whisk the cake flour, baking powder, baking soda, and salt for about 30 seconds to distribute the leaveners. Transfer 1 tablespoon of this measured mixture to a separate small bowl. Add the blueberries and toss gently until they have a thin, even coating. This light flour coating helps absorb surface moisture and makes it easier to distribute the fruit without crushing it.
  4. Place the softened butter and granulated sugar in the bowl of a stand mixer fitted with the paddle, or use a large bowl and hand mixer. Beat on medium speed for 3 minutes, scraping the bowl halfway through, until the mixture looks pale, fluffy, and increased in volume. Add the eggs one at a time, beating for about 30 seconds after each addition. Mix in the vanilla, then scrape the bowl and paddle thoroughly.
  5. With the mixer on low, add one-third of the remaining dry mixture and mix just until mostly incorporated. Add half the buttermilk in a slow stream, followed by another third of the dry mixture, the remaining buttermilk, and the final dry ingredients. Stop while a few flour streaks remain. Fold with a flexible spatula until the batter is smooth and thick, then gently fold in the coated blueberries without crushing them or overworking the flour.
  6. Spread the batter evenly in the prepared pan, working it into the corners with an offset spatula. Scatter the chilled streusel over the surface, keeping some larger clusters intact and covering the batter without pressing down. Bake for 45 to 52 minutes, rotating the pan once after 35 minutes. The cake is done when the center is golden and springs back lightly, and a skewer inserted away from a berry comes out with moist crumbs but no wet batter.
  7. Transfer the pan to a wire rack and cool the cake in the pan for 60 minutes. Run a thin knife along the two unlined edges, then use the parchment sling to lift the cake carefully onto the rack. Let it cool for at least 30 minutes more before cutting into 12 pieces. This cooling period allows the crumb and blueberry juices to set while preserving the contrast between the soft cake and crisp topping.

Notes

  • Use a light-colored metal pan for steady heat conduction. A dark pan can brown the edges and streusel before the center has finished baking, while a glass pan responds more slowly to temperature changes.
  • Stop creaming after the butter and sugar become pale and aerated. If the butter begins looking shiny or greasy, it has become too warm and will hold less air in the batter.
  • Mix only until the final flour streaks disappear. Continued beating after the flour is hydrated develops gluten and can turn the intended tender crumb springy or tunneled.
  • Keep frozen blueberries in the freezer until the moment they are coated and folded in. Thawing releases juice that can loosen the batter and create heavy purple patches.
  • Check the center rather than relying only on browned edges. Insert the skewer away from visible berries because puncturing a berry can resemble raw batter and lead to unnecessary overbaking.