Combine warm water, sugar, and yeast in a bowl and let it sit for 5 minutes until frothy.
Add bread flour, all-purpose flour, salt, and 4 tablespoons olive oil to the yeast mixture and mix until a dough forms.
Knead the dough on a floured surface for 8 to 10 minutes until smooth.
Place the dough in a greased bowl, cover, and let it rise for 1 hour until doubled in size.
Preheat the oven to 375°F (190°C).
Punch down the dough and spread it onto a greased baking sheet.
Make indentations in the dough and fill each with raspberry preserves.
Let the dough rise for another 30 minutes.
Bake for 25 to 30 minutes until golden brown.
Mix confectioners' sugar with whole milk to make a glaze, then drizzle over the focaccia once cooled.