Preheat the oven to 200°C fan and line 10 holes of a muffin tin with deep holes.
Mix the milk with the lemon juice and set aside for 10 minutes so it curdles.
For the crumble, rub all ingredients together until you get small clumps. Set aside.
In a bowl, whisk the eggs with the sugar. Add yogurt and the curdled milk and beat again, then add the melted butter and vanilla and combine.
In another bowl, mix the flour, oats, baking powder and salt.
Fold the dry ingredients into the wet mixture until just combined.
Toss the frozen blueberries in 1 tablespoon of flour and fold through the dough.
Divide the batter between the muffin cases add a spoonful of crumble on top.
Bake for 5 minutes at 200°C fan, then reduce to 160°C fan and bake for another 45 minutes until golden and risen.
Leave to cool on a wire rack before serving.