In a stand mixer bowl, combine warm water and sugar. Sprinkle in active dry yeast, whisk gently, and let sit for about 5 minutes.

Attach the dough hook and gradually add bread flour, all-purpose flour, and salt. Mix on low speed until sticky dough forms, about 3-5 minutes.

Transfer the dough into an oiled bowl, cover with plastic wrap, and let it rise for about 1 hour until doubled.

Grease a 9x13-inch baking pan generously with olive oil.

Transfer the risen dough to the greased pan, fold and knead lightly, cover, and let it rise again for another hour.

Preheat the oven to 425°F (220°C). Poke deep dimples into the dough and spread raspberry preserves on top.

Bake for 18-22 minutes until golden brown, then remove and poke additional holes, filling them with more preserves.

Mix confectioners' sugar with whole milk until smooth. Drizzle the glaze over the warm focaccia and cut into squares.