Combine the pineapple juice, milk, instant yeast and brown sugar in the bowl of a stand mixer fitted with a dough hook*. Add the flour, sourdough discard, beaten egg, vanilla extract and salt. With the mixer on low, slowly pour in 2 Tablespoons of melted butter. Increase speed to medium and mix until a shaggy dough forms, about 2 minutes.

Transfer the dough to a smooth work surface and knead until smooth, about 3-4 minutes. The dough should be smooth, soft and just slightly tacky (not sticky). If needed, add more flour or milk (1 Tablespoon at a time) to reach your desired consistency.

Transfer the dough to a large oiled bowl and cover with plastic wrap. Let rise for 90 minutes, or until doubled in size.

Brush a 9x13-inch baking pan with the remaining 1 Tablespoon of melted butter and set aside.

Turn the dough onto a smooth work surface and divide into 15 equal-sized pieces. This doesn't have to be exact, but if you do want perfectly identical rolls, weigh the dough on a kitchen scale and divide that number by 15. For me, each roll weighs about 73 grams.Using your palm for friction, roll each piece of dough into a ball, then place the rolls into the prepared baking pan with the seam-side down. Repeat until you have 15 rolls.

Cover the baking pan with plastic wrap or a clean kitchen towel and let the rolls rise for 60 minutes until puffed and doubled in size.

Preheat the oven to 375℉. Lightly brush the rolls with egg wash. Bake for 20-25 minutes until golden brown. Let cool slightly in the pan, then brush with 1 Tablespoon melted butter before serving (optional).