Preheat oven to 150°C. Butter and line an 20cm round cake tin with baking paper.
Whisk flour, poppy seeds, salt and baking powder in a large bowl. In a separate bowl, cream the butter and sugar for 5 minutes with an electric beater until pale and fluffy. Add vanilla, eggs, crème fraiche, orange juice and zest. Beat until smooth.
Fold the flour mixture and blueberries in the wet batter gently until thoroughly combined. Bake in the pre-heated oven for approximately 80 minutes until golden, cooked through the middle when tested with a skewer and coming away from the edges.
Remove from the oven and allow to cool in the pan for 30 minutes. Carefully, remove from the pan and store in a cool corner of your kitchen for up to 3 days.
Notes
Flour - Substitute unbleached spelt flour with wholemeal flour. You can also use plain flour.
Crème Fraiche - Crème Fraiche can be substituted with sour cream or thick Greek yoghurt.
Blueberries - Frozen blueberries can be swapped for fresh ones.