Whisk flour, baking powder, baking soda, salt, and cinnamon together in a large bowl. In a medium bowl, whisk buttermilk, lemon zest and juice, and vanilla. In a third bowl, whisk eggs and yolk to combine.

Using a stand mixer, beat butter and sugar on medium-high speed until pale and fluffy, about 3 minutes. Reduce speed and add half of eggs until incorporated. Repeat with remaining eggs.

Reduce speed to low and add one-third of flour mixture, followed by half of buttermilk mixture, mixing until just incorporated after each addition.

For the filling, whisk sugar, pectin, and salt together in a small saucepan. Process blueberries in a blender until mostly smooth. Heat sugar-blueberry mixture until just simmering, about 3 minutes. Let cool for 5 minutes.

Spoon half the batter into the prepared pan. Create a channel in the center and spoon half of the filling into the channel. Swirl the filling into the batter. Repeat with remaining batter and filling.

Bake for 60 to 70 minutes until golden brown. Cool the cake in the pan for 10 minutes, then invert onto a wire rack and cool for at least 3 hours before serving.