Prepare the Dough:

1. Activate the Yeast: In a small bowl, combine the warm milk, sugar, and yeast. Stir and let it sit for 5-10 minutes until it becomes frothy.
2. Mix the Dough: In a large bowl, whisk together the flour and salt. Add the activated yeast mixture, melted butter, eggs, and vanilla extract. Mix until the dough begins to come together.
3. Knead the Dough: Transfer the dough to a floured surface and knead for 5-7 minutes until the dough is smooth and elastic.
4. Let the Dough Rise: Place the dough in a greased bowl, cover with a kitchen towel, and let it rise in a warm place for about 1 hour, or until it has doubled in size.

Prepare the Custard Filling:

5. Make the Custard: In a medium saucepan, combine the cream, milk, sugar, and cornstarch. Whisk the egg yolks in a separate bowl and gradually add a bit of the warm milk mixture to temper the eggs.
6. Cook the Custard: Pour the tempered egg mixture back into the saucepan with the rest of the milk mixture. Cook over medium heat, whisking constantly, until the custard thickens, about 5-7 minutes. Remove from heat and stir in the vanilla extract. Let it cool.

Prepare the Raspberry Filling:

7. Cook the Raspberries: In a small saucepan, combine the raspberries, sugar, and lemon juice. Cook over medium heat for about 5-7 minutes, mashing the berries with a spoon until they form a thick syrup. Set aside to cool.

Assemble the Buns:

8. Shape the Dough: After the dough has risen, punch it down and divide it into 12 equal portions. Roll each portion into a ball and flatten it into a disc shape.
9. Fill the Buns: Spoon a small amount of custard filling into the center of each dough disc, then add a teaspoon of raspberry filling on top of the custard. Pinch the edges of the dough together to seal the bun.
10. Place in a Baking Dish: Arrange the filled buns in a greased baking dish, leaving some space between each one. Cover with a towel and let them rise for another 30 minutes.
11. Bake the Buns: Preheat the oven to 350°F (175°C). Bake the buns for 25-30 minutes, or until golden brown.