Warm 1 cup of full-fat cow milk to about 110°F in a small saucepan. Sprinkle 2 teaspoons of dry active yeast into the milk and let it sit for 5 minutes until frothy.

Combine 3 cups of all-purpose flour and ¼ cup of white sugar in a large mixing bowl. Pour in the yeast mixture and ¼ cup of softened butter, mixing until a dough forms. Knead for 8 minutes until smooth, then cover and let it rise in a warm place for 3 hours.

In a medium saucepan, whisk together 1 cup of heavy cream, ¼ cup of sugar, and 2 tablespoons of cornstarch. Cook over medium heat, stirring continuously, until thickened, about 5-7 minutes. Remove from heat and stir in 1 tablespoon of vanilla extract. Allow to cool.

Punch down risen dough and roll into a rectangle about ½ inch thick. Spread cooled vanilla cream, leaving a 1-inch border. Spoon dollops of strawberry jam, roll tightly into a log, and cut into 12 pieces. Place cut-side up on a greased baking tray.

Combine ¼ cup softened unsalted butter, ¼ cup sugar, and ½ cup all-purpose flour in a bowl, mix until crumbly. Sprinkle evenly over the buns.

Preheat oven to 350°F. Bake for 25-30 minutes until puffed and golden brown. Let cool slightly on a wire rack before serving.