POLENTA: Preheat the oven to 350 degrees. Lightly coat a 8 x 8 inch baking dish with cooking spray and set aside.
Combine the polenta, water, and kosher salt in a 2-quart baking dish. Stir together, and place in the oven. Bake 50 minutes. Remove from the oven, stir in the butter and return to the oven for 10 more minutes. Remove from the oven and stir again. Return to the oven for 10 minutes. Remove from the oven, and stir in the Parmesan. Pour into the prepared 8 x 8 inch baking dish and smooth the top. Let cool to room temperature, then cover and refrigerate until firm, about 2 hours.
Preheat the oven to 375 degrees. Oil a 2-quart gratin dish. Cut the polenta into squares or rectangles, and arrange the polenta in the dish, overlapping the pieces slightly. Spread the tomato sauce over the slices, and sprinkle with Parmesan. Drizzle olive oil over the top.
Bake for 15 to 20 minutes, until sizzling. Remove from the heat and serve with Tuscan White Beans.
TUSCAN WHITE BEANS: Rinse beans with cool water, removing any broken, blistered, or brown beans. Drain.
Soak the beans: In a large bowl, cover beans by 3 inches with cold water, cover and set aside at room temperature for 8 hours or overnight, up to 12 hours (soaking for longer will cause the beans to absorb too much liquid and loose their texture and flavor). If preparing more than 12 hours in advance, drain the soaked beans, then refrigerate until ready to use. {For a quicker soak in place of the overnight soaking}: In a large pot, cover beans by 3 inches with cold water, cover and bring to a boil. Boil for 1 minute, remove pot from heat and set aside, covered, for 1 hour.
Place the soaked beans in a large pot and cover with water to 3/4 inch above the level of the beans. Bring to a boil. Once beans are boiling, skim off any foam that has risen to the surface. Add sage, then reduce heat so that the beans bubble steadily, but not vigorously. Cover loosely.
Continue to cook, stirring occasionally until the beans begin to soften, 30 to 45 minutes. If the beans become dry while cooking, add water one cup at a time as needed. Once the beans are soft, add kosher salt and pepper. Continue to cook until the beans are very tender, about 15 additional minutes.
Drain any excess cooking liquid. Stir in garlic and olive oil. Serve with baked polenta.
Notes
Suggested meal planning: Don't be fooled by the large amount of prep and cook time-it is almost entirely inactive. Relax and let the slow cooking happen in the background. The night before, soak the white beans and prepare the polenta up through Step 2. The next morning, drain the beans and place in the refrigerator. A little more than an hour before you are ready to serve, begin to cook the beans. While beans are boiling, preheat oven for the polenta, slice and arrange polenta slices. About 20 minutes before the beans are ready (Step 5), top polenta slices with tomato sauce, Parmesan, and olive oil and place in the oven. Finish beans, remove polenta from the oven, and serve.
To prepare in advance: The cooked polenta (through Step 2) can be stored in the refrigerator for up to 4 days. After soaking but prior to cooking, the white beans can be refrigerated for up to 3 day; fully prepared, the Tuscan white beans can be refrigerated for up to 5 days.