Combine warm water and sugar in a mixing bowl, then sprinkle in yeast. Allow to sit for 5 minutes until bubbly.

In a stand mixer, mix bubbly yeast mixture with bread flour, all-purpose flour, and salt using a dough hook on low until sticky, about 3-5 minutes.

Grease a bowl with olive oil, transfer dough, cover, and let it rise in a warm area until doubled in size, about 1 hour.

Grease a 9x13-inch baking pan with remaining olive oil. Punch down the dough, transfer to pan, cover, and let rise for another hour.

Preheat the oven to 425°F (220°C).

Poke holes in the dough, spoon raspberry preserves over the surface, ensuring not to overcrowd.

Bake in the preheated oven for 18-22 minutes until golden brown and hollow-sounding when tapped.

Prepare glaze by mixing confectioners' sugar with milk to desired consistency.

Once cooled, drizzle glaze over focaccia, slice, and serve fresh.