Step 1: In a saucepan, heat the heavy cream over medium heat until it begins to simmer.
Step 2: In a bowl, whisk the granulated sugar (for custard) and egg yolks until smooth. Gradually add about half of the hot cream to the egg mixture, whisking constantly to temper the yolks.
Step 3: Return the tempered mixture to the saucepan with the remaining cream and cook over low heat, stirring constantly, until the custard thickens and coats the back of a spoon.
Step 4: Remove from heat and stir in the vanilla extract (for custard). Transfer to a clean bowl, cover the surface directly with plastic wrap, and let the custard cool to room temperature, then chill in the refrigerator.
Step 5: Preheat oven to 350°F (175°C). Grease a 12-cup muffin tin.
Step 6: In a large bowl, combine all-purpose flour, granulated sugar (for buns), baking powder, and salt. Mix until well combined.
Step 7: In another bowl, whisk the softened butter, eggs, milk, vanilla extract (for buns), and shredded coconut. Add the wet ingredients to the dry ingredients and mix until just combined; do not overmix.
Step 8: Spoon the batter into the greased muffin tin, filling each cup about two-thirds full.
Step 9: Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean. Let cool in the tin for a few minutes, then transfer to a wire rack to cool completely.
Step 10: Once buns are cooled, cut each in half horizontally.
Step 11: Spread the chilled custard cream generously on the bottom half of each bun. Replace the top half.
Step 12: Garnish the buns with chopped nuts, granola, fresh berries (if using), and a dusting of powdered sugar (if using). Serve immediately and enjoy!