In a large mixing bowl, combine your sourdough discard with lukewarm milk, melted unsalted butter, pineapple juice, and egg. Mix until smooth. Gradually add in brown sugar, salt, instant yeast, and all-purpose flour. Stir until a shaggy dough forms, then knead for about 8 minutes by hand or in a stand mixer.

Cover the bowl tightly with plastic wrap or a damp kitchen towel and let the dough rise in a warm place for 1.5 to 2 hours, or until doubled in size.

Once the dough has risen, gently punch it down. Transfer to a floured surface and divide into 9, 12, or 16 equal pieces. Shape each into a ball and place seam-side down.

Line a baking sheet with parchment paper and arrange the shaped rolls closely without touching. Cover them lightly and let rise for 40 minutes to 1 hour.

Preheat your oven to 350°F (180°C). Mix melted butter and egg yolk; brush over the rolls. Bake for 20-25 minutes until golden brown.

Remove from the oven and let cool for about 10 minutes before transferring to a wire rack or enjoying warm.