Step 1

To make the starter: Mix the water and yeast. Weigh your flour; or measure it by gently spooning it into a cup, then sweeping off any excess. Add the flour, stirring until the flour is incorporated. The starter will be paste-like; it won't form a ball.

Step 2

, Cover and let rest at room temperature for 10 to 14 hours; overnight works well.

Step 3

, To make the dough: Combine the starter with the remaining dough ingredients. Mix and knead — by hand, mixer, or bread machine set on the dough cycle — to make a dough that’s soft, smooth, elastic, and sticky. If you're kneading in a stand mixer, it should take about 6 to 8 minutes at medium speed. Stop the mixer and scrape down the sides of the bowl as needed; the dough won’t completely clean the sides of the bowl, but remain sticky throughout kneading.

Step 4

, Place the dough in a greased bowl, cover, and let rise until doubled in bulk, about 1 hour.

Step 5

, Use non-stick vegetable oil spray to grease a 9” x 13” pan. Drizzle 1 tablespoon olive oil atop the spray; the spray keeps the bread from sticking, while the olive oil gives the bottom crust great crunch and flavor.

Step 6

, To shape the focaccia: Transfer the dough to the prepared pan and gently stretch it into the corners. If the dough doesn’t reach the edges of the pan, cover and let rest for 15 minutes before continuing to stretch it to fill the entire pan.

Step 7

, Cover the pan and allow the dough to rise for 30 minutes.

Step 8

, In a small bowl, combine the baking soda and hot water to make the wash, stirring to dissolve. Brush all of the wash over the surface of the dough. Be generous with your application; it’s fine if some of the wash drips down the edges into the pan.

Step 9

, Use your fingers to make irregularly spaced dimples in the dough, pressing down firmly; your fingers should reach the bottom of the pan without actually breaking through the dough.

Step 10

, Re-cover the dough and let it rise until it's noticeably puffy, about 45 to 60 minutes. The dough should have expanded, but shouldn't seem fragile nor look like it might collapse.

Step 11

, Toward the end of the rising time, preheat the oven to 425°F.

Step 12

, To top the focaccia: Before baking, brush the focaccia with the egg wash, then sprinkle with salt. The top of the dough will be quite wet but don’t worry – any excess moisture will bake off in the oven.

Step 13

, To bake the focaccia: Bake the focaccia until the top is dark brown and the bottom is golden (you can use an offset spatula or fork to lift the bread to peek at the bottom), about 24 to 30 minutes.

Step 14

, Remove the focaccia from the oven and immediately transfer it from the pan to a cooling rack. Brush the top of the warm focaccia with the melted butter.

Step 15

, Serving and storage information: Enjoy focaccia warm from the oven. It’s best the same day it's made, but leftovers can be successfully reheated, either as slices in the toaster or in a 350°F oven just until warmed through.