Put 1 3/4 cups warm (about 110°) water in a medium bowl and sprinkle with yeast. Wait until yeast dissolves and foams, about 10 minutes.
In the bowl of a stand mixer using the paddle attachment, mix flours and fine salt. Add yeast mixture and 2 tbsp. oil and mix until a rough ball of dough forms, about 1 minute.
Add 2 tsp. oil to a large bowl and rub all over inside. Add dough and turn to coat on all sides. Cover with plastic wrap and a kitchen towel and let rise in a warm place until doubled, about 2 1/2 hours.
Drizzle about 1 tsp. oil into each of 4 (6-in.) cake pans and rub over bottom and sides. Punch down dough, divide into 4 equal portions, and put each in a pan. Using your fingertips, stretch dough to cover bottom of pan. Cover pans with kitchen towels and let rest in a warm place until almost doubled, about 1 hour.
Preheat oven to 400°. Drizzle about 1 tbsp. oil over each loaf and spread gently to cover loaf. Using your fingertips, poke indentations all over surface of focaccia, about 1 in. apart.
For squash focaccia: Cut squash slices into quarters and put in a bowl. Add maple syrup, the 1 tsp. olive oil, paprika, and kosher salt to taste, and massage into squash. Arrange squash on surface of a focaccia and sprinkle with thyme leaves.
For grape focaccia: Arrange grapes and rosemary leaves over focaccia.
For tomato-garlic focaccia: Arrange whole cluster of tomatoes, garlic slices, and thyme leaves over focaccia. Brush tomatoes with oil.
For olive-pepper focaccia: Arrange olives, chopped rosemary, and peppers over focaccia.
Sprinkle focaccias with flake sea salt to taste. Slide them into oven and immediately reduce heat to 375°. Bake until golden brown, about 40 minutes, checking halfway through. If not golden brown after 40 minutes, broil 30 seconds to 2 minutes to brown top (baking longer will make focaccias dry). Let sit in pans 5 minutes.
Loosen focaccias from cake pans with a thin metal spatula, then carefully lift onto a wire rack to cool slightly. Eat warm or at room temperature.
*Fined brined sweet cherry peppers in jars at well-stocked grocery stores. They're often found in grocery store salad bars too. Find Jacobsen flake sea salt, handcrafted on the Oregon coast, at well-stocked grocery stores throughout the West and on jacobsensalt.com.
Nutritional analysis per slice SQUASH FOCACCIA: Calories 180 (27% from fat); Protein 4.5g; Fat 5.3g (sat 0.8g); Carb 30g; Fiber 2.7g; Sodium 282mg; Chol 0mg
Nutritional analysis per slice GRAPE FOCACCIA: Calories 180 (21% from fat); Protein 4.5g; Fat 4.2g (sat 0.6g); Carb 33g; Fiber 2.6g; Sodium 282mg; Chol 0mg
Nutritional analysis per slice TOMATO-GARLIC FOCACCIA: Calories 182 (32% from fat); Protein 4.5g; Fat 6.5g (sat 0.9g); Carb 27g; Fiber 2.5g; Sodium 282mg; Chol 0mg
Nutritional analysis per slice OLIVE-PEPPER FOCACCIA: Calories 195 (36% from fat); Protein 44g; Fat 7.9g (sat 0.6g); Carb 28g; Fiber 2.4g; Sodium 750mg; Chol 0mg