Warm the milk lukewarm. Pour the flour into a bowl and make a depression in the middle. Crumble the yeast into the lukewarm milk and dissolve it while stirring. Pour yeast milk into the hollow, stir with some flour from the rim.
Cover and leave to rise in a warm place for about 15 minutes.
Add sugar, eggs, salt and butter to the pre-dough. First use the dough hooks of the hand mixer, then work into a smooth dough with your hands. Cover the dough and let it rise for about 30 minutes in a warm place.
Peel and quarter the pears and remove the core. Cut quarters into small cubes and sprinkle with lemon juice. Defrost blueberries in a sieve.
Briefly knead the yeast dough and roll out into a rectangle (approx. 40 x 45 cm) on the floured work surface. Spread the jam on top, leaving an approx. 2 cm wide edge all around.
Sprinkle pear cubes and blueberries one after the other on the coated dough surface. Roll up the dough from the long side, pressing the open sides. Cut the roll with a saw knife into approx. 16 slices.
Spread the slices on 2 baking trays lined with baking paper. Cover and leave to rise for about 10 minutes.
Bake in the preheated oven (electric cooker: 200 °C/ convection oven 175 °C/ gas: see manufacturer) for 25-30 minutes one after the other, remove from oven and allow to cool.