Preheat the oven to 350 °F (175 °C) and generously grease and flour a 9-inch Bundt pan.

Beat the white sugar and softened butter with an electric mixer until pale and airy, then blend in the eggs one at a time, ensuring each is fully incorporated.

Mix in the sour cream and vanilla, combining until smooth.

Whisk the flour with the baking powder and salt, then fold this dry mixture into the batter just until no streaks remain; gently fold in the blueberries.

Spread half of the batter evenly in the prepared pan.

Stir together the brown sugar, pecans, and cinnamon, sprinkle half of this streusel over the batter, and spoon the remaining batter on top; cover with the rest of the streusel and lightly swirl it through the batter with a thin knife.

Bake until a skewer inserted in the center emerges clean, 60 – 75 minutes, and cool the cake in the pan for a short while before inverting onto a wire rack.

Transfer to a serving plate once barely warm and sift confectioners’ sugar over the top just before slicing.