In a small bowl, stir together milk, melted butter, yeast, and sugar. Let stand until mixture is foamy, 5 to 10 minutes.
In the bowl of a stand mixer fitted with a dough hook attachment, whisk together by hand flour and salt. Add milk mixture to flour mixture. With mixer at low speed, knead with dough hook until a soft, elastic, and slightly sticky dough forms, approximately 15 minutes, stopping to scrape down sides and bottom of bowl as needed.
Lightly oil a large bowl.
Turn out dough onto a lightly floured surface and shape into a smooth round. Place dough in bowl, turning to grease top. Cover and let rise in a warm (85°F), draft-free place until doubled in size, 30 minutes to 1 hour.
Line a large, rimmed baking sheet with parchment paper.
Punch down dough and let rest for 10 to 15 minutes. On a lightly floured surface, divide dough into 12 equal pieces. Roll each portion into a smooth, round ball. Place on prepared baking sheet, 2 inches apart. Loosely cover with plastic wrap and let rise in a warm, draft- free place until almost doubled in size, 30 to 45 minutes.
Preheat oven to 375°F. Bake rolls until lightly golden and an instant-read thermometer inserted in the centers registers 190°F, 9 to 10 minutes. Let cool on baking sheet for 5 minutes. Transfer to a wire rack and let cool completely.
To fill, using a serrated bread knife in a gentle sawing motion, make a cut a third of the way down the front of each bun, cutting at an angle toward the back of bun, making sure not to cut all the way through.
Spread a layer of room temperature butter onto bottom cut side of each bun. Top butter layer of each bun with 1 tablespoon Preserve Filling.
Place Elderflower Whipped Cream in a piping bag fitted with a star tip (Wilton #32) and pipe desired amount of whipped cream over Preserve Filling. (There will be whipped cream left over.)
Garnish with confectioner’s sugar, if desired. Serve immediately.
Notes
Make-Ahead Tip: Buns can be prepared and baked up to a day in advance and stored in an airtight container at room temperature. For best presentation, split and fill no sooner than 30 minutes before serving.
Recipe by TeaTime Magazine at https://teatimemagazine.com/cornish-splits/