Ingredients

Scale

Cake base:

1½ cups (190g) all-purpose flour
1½ tsp baking powder
¼ tsp salt
½ cup (1 stick / 115g) unsalted butter, softened
¾ cup granulated sugar
2 large eggs
1 tsp vanilla extract
½ cup buttermilk (or whole milk + 1½ tsp vinegar)
1½ cups fresh blueberries (tossed in 1 tbsp flour to prevent sinking)

Cinnamon-sugar swirl:

¼ cup packed brown sugar
1 tsp cinnamon

Streusel topping (you love buttery crunch!):

¼ cup all-purpose flour
¼ cup packed brown sugar
½ tsp cinnamon
3 tbsp cold unsalted butter, cubed
Pinch of salt

Instructions

1. Prep:

Preheat oven to 350°F (175°C). Grease a 10″ cast-iron skillet or 9×9″ baking dish.
Toss blueberries with 1 tbsp flour; set aside.

2. Make cake batter:

Whisk flour, baking powder, and salt in a bowl.
Beat butter and granulated sugar until light (~2 min). Add eggs one at a time, then vanilla.
Alternate adding dry ingredients and buttermilk, beginning and ending with dry. Mix until just combined.
Fold in floured blueberries.

3. Swirl & top:

Pour batter into skillet. Sprinkle cinnamon-sugar evenly over top; swirl gently with a knife (4–5 figure-8 motions).
Make streusel: Mix flour, brown sugar, cinnamon, and salt. Cut in cold butter with fingers or fork until crumbly. Sprinkle over batter.

4. Bake:

Bake 35–40 minutes until golden and toothpick comes out clean (avoid blueberry pockets). Cool 15 minutes before serving.

💡 Pro Tips for Perfection:
✅ Flour the blueberries—prevents sinking to bottom (critical for even distribution!).
✅ Don’t over-swirl—4–5 passes max for defined cinnamon pockets (not a muddy mess).
✅ Blood sugar friendly (you love this!):
→ Cake: 1½ cups almond flour + ¼ cup coconut flour + ¾ cup monk fruit blend
→ Swirl/Streusel: ¼ cup allulose brown sugar substitute + 1 tsp cinnamon + 3 tbsp melted butter
→ Net carbs: ~6g/slice
✅ Keto version: Follow blood sugar swaps above; add 1 tbsp xanthan gum to dry ingredients.
✅ Extra decadence:
→ Drizzle with lemon glaze (1 cup powdered erythritol + 2 tbsp lemon juice)
→ Serve with whipped cream sweetened with vanilla stevia
✅ Make ahead: Cake keeps 3 days room temp (cover tightly), 5 days refrigerated, or freeze unfrosted slices 3 months.

Prep Time & Nutrition (per slice, 8 servings):