In a small saucepan, heat the cream with the sugar, vanilla extract, and half of the milk until it comes to a boil. In a separate bowl, whisk together the cornstarch, egg yolk, and remaining milk. Slowly pour the starch mixture into the boiling cream while whisking constantly until it thickens into a smooth pudding. Remove from heat and let cool completely. Set aside for later.

Gently warm the milk to 38°C / 100°F and stir in the yeast and 1 tablespoon of the sugar. Let it sit for a few minutes until slightly foamy. In a large mixing bowl, combine the flour, remaining sugar, egg, soft butter, and salt. Add the yeast mixture and knead for about 10 minutes until you get a smooth, soft dough that doesn’t stick. Cover the bowl tightly with plastic wrap and let rise in a warm spot for 90 minutes.

Combine the butter, sugar, flour, vanilla extract and a pinch of salt and mix until crumbly. Chill the streusel until ready to use.

Once the dough has risen, knead it briefly and divide into 12 equal balls, about 80g / 3oz each. Line a rectangular baking dish with parchment paper and arrange the dough balls inside. Let them rest for 20 minutes.

Use your thumbs and press in the middle of the dough ball to form kind of a bowl shape that is going to be filled each with 1 tablespoon of vanilla pudding and 1 heaping teaspoon of strawberry jam side by side.

Preheat the oven to 180°C / 350°Ft. Sprinkle the chilled streusel generously over the buns and bake for about 55 minutes, or until golden. Serve slightly warm or fully cooled—both are delicious. Finish with a dusting of powdered sugar before serving.