Chop the yellow onion and celery stalks on a wooden cutting board using a sharp chef knife. Aim for uniform pieces about one-quarter inch thick so they cook evenly later on. You will smell the sharp aroma of the fresh onion immediately as you work. The celery should look bright green and feel completely crisp under your knife blade. Keep the sizes irregular to add a nice homemade feel to the final texture. (I tried using a food processor once but it turned the vegetables into mush and ruined the dish.) Small knife cuts are the fix.

Melt the unsalted butter in a ten-inch cast-iron skillet over medium heat (about 5 on a 10-dial). Add the diced yellow onion and celery then cook for 8 to 10 minutes while stirring frequently with a wooden spoon. You will hear a gentle sizzling sound as the water escapes and the vegetables begin to soften. The onion pieces will look translucent and glossy while the celery turns a slightly deeper shade of green. Do not let the vegetables brown or get dark edges during this phase. Cook gently over medium heat, soft vegetables blend seamlessly into the liquid base later.

Place the cubed sourdough bread into a large clear glass mixing bowl and add the chopped fresh sage and fresh thyme. Pour the warm sautéed vegetables and melted butter directly over the bread cubes then fold gently with a rubber spatula in a J-shaped motion. You will notice the dry bread immediately starts soaking up the rich melted butter. The bright green flecks of sage and thyme will distribute unevenly across the surfaces of the white bread cubes. Work slowly so you do not crush the bread cubes into crumbs. Combine thoroughly in the bowl, even distribution ensures every single bite has plenty of herbal flavor.

Pour the chicken broth over the bread mixture in three separate additions while tossing lightly between each pour. Let the mixture rest for 5 minutes off the heat so the liquid absorbs fully into the center of each cube. The bread will shrink slightly in volume and look wet but it should not be swimming in a pool of liquid. You will smell the rich chicken stock blending with the sage and buttery onions. Miss this absorption window and the broth will simply collect at the bottom of your baking pan. Rest 5 minutes before baking, this gives the liquid time to saturate the starch so it stays moist.

Transfer the mixture into a rectangular white ceramic baking dish and spread it into an uneven layer. Bake at 375°F for exactly 30 minutes until the top turns deep golden brown. You will hear the edges bubbling gently and a thin crisp crust will form on the exposed bread tops. The kitchen will fill with an incredibly warm roasted poultry and herb aroma. Go past 35 minutes and the top will scorch and turn bitter. Bake at 375°F, steady heat crisps the top while keeping the inside perfectly soft.