Preheat oven to 180°C (160°C fan). Grease and line a loaf tin.
Rub the sugar and orange zest together with your fingers to release the citrus oils. Add the butter and cream by hand until pale and fluffy.
Mix in the amasi, orange juice, and vanilla essence.
Sift together the cake flour, baking soda, baking powder, and salt in a separate bowl. Stir through the poppy seeds.
Fold the dry ingredients into the wet mixture in two or three goes, until just combined.
Fold in the blueberries gently, straight from frozen if using.
Pour into the tin and smooth the top.
Bake for 50–60 minutes, until a skewer comes out clean.
Cool in the tin for 10 minutes, then transfer to a wire rack.