Fresh thyme pairs surprisingly well with juicy plums and adds a welcome savory note to this sweet focaccia.
In a large bowl, whisk together flour, yeast, 2 tablespoons granulated sugar, 1 tablespoon salt, and 1 tablespoon thyme. Add cold water and 1/3 cup oil. Stir with a wooden spoon or your hands until a wet dough forms and no dry flour remains. Cover bowl with plastic wrap and let rise at room temperature until dough quadruples in volume and top appears bubbly, at least 12 hours and up to 18 hours.
Pour 1/3 cup oil onto a 12-by-18-inch rimmed baking sheet. Lightly coat your hands with oil on sheet, and scrape dough onto center of sheet. Turn dough to evenly coat with oil, then press to spread in an even thickness to edgesof pan. Use your fingers to make dimple-like indentations all over dough. Cover and let rise at room temperature until doubled in volume (dough should reach top of sheet rim), about 1 1/2 hours.
Preheat oven to 500 degrees with rack in lower third. In a bowl, toss plums with remaining 2 tablespoons granulated sugar, 2 teaspoons thyme, and 1/4 teaspoon salt. Scatter evenly over dough; drizzle with any accumulated juices from bowl. Sprinkle the top evenly with pearl sugar.
Bake until puffed slightly and golden brown on top, 16 to 18 minutes (if top is browning too quickly, tent with foil). Let focaccia cool in pan on a wire rack until warm but no longer hot, about 20 minutes. Serve warm or room-temperature, or let cool completely and store in an airtight container at room temperature up to 2 days.
Pearl sugar is available at baking-supply stores or kingarthurflour.com.