In a large bowl, combine the warm water, granulated sugar, and yeast. Let the mixture rest for about 5 minutes, or until the yeast begins to bloom.

Pour half of the vegetable oil into the yeast mixture, reserving the rest. Add the flour and kosher salt, stirring until it comes together.

Transfer the dough to a lightly greased bowl, cover it with a kitchen towel, and let it rise in a warm place for 1 hour, or until it has doubled in size.

While your dough rises, preheat your oven to 450 degrees F (232 degrees C).

Pour the remaining oil into a 9x11 inch baking pan, using a pastry brush to evenly coat the bottom of the pan.

Once the dough has risen, carefully transfer it to the prepared baking pan, using your fingertips to gently spread it out to the edges.

In a medium bowl, mix together the melted butter, brown sugar, ground cinnamon, and vanilla. Fold in the diced apples until they are evenly coated.

Spread 1/3 of the apple mixture evenly over the dough. Gently fold the edges of the dough over the filling, flipping it seam side down. Press and stretch the dough to spread it out.

Create deep dimples all over the surface of the dough with your fingertips.

Spread the remaining apple mixture over the top and bake for 28-30 minutes.

While the focaccia bakes, whisk together confectioners' sugar and milk in a small bowl, adding milk gradually until you reach your desired glaze consistency.

Once the focaccia is golden and baked through, let it cool slightly in the pan before drizzling the glaze over the warm focaccia.

Slice it up and serve warm—prepare for happy faces!