In a mixing bowl, combine warm water, granulated sugar, and active dry yeast. Mix well and let it sit for 10 minutes.

Once the yeast mixture is bubbly, add the egg and milk. Mix until well combined.

Add all-purpose flour, granulated sugar, and room temperature butter. Mix until incorporated.

Knead the dough in a stand mixer on medium-low speed for about 15 minutes.

Transfer the dough to a bowl, cover with plastic wrap, and proof at 28°C (82°F) for about 2 hours or until doubled in size.

Once proofed, pour the dough into a prepared square pan using a spatula. Drizzle generously with melted butter.

Use your fingers to gently press dimples into the surface of the dough.

Proof again for about 45 minutes at 28°C (82°F).

Dimple the dough again carefully and pour any remaining melted butter on top.

Preheat the oven to 180°C (356°F). Bake the focaccia for 23–25 minutes, checking at the 20-minute mark.

While it bakes, prepare the glaze by sifting powdered sugar and whisking it with milk until smooth.

Once baked, transfer the focaccia to a cooling rack and let it rest for 5 minutes.

Pour the glaze over the warm focaccia and let it sit for 15 minutes to set.