3 pounds Yukon Gold or other yellow potatoes, peeled
1 pound fennel bulbs, trimmed
Preheat oven to 400°F and grease 3-1/2 quart oval or rectangle baker with 1 teaspoon of butter. Set aside.
Using the metal "s" blade, process bread crumbs in Cuisinart Food Processor until coarse (usually takes about 30-40 seconds). Add the rest of the butter as well as Parmigianno-Reggiano to work bowl for about another 30-40 seconds, or until crumbs are somewhat fine. Remove contents from bowl and set aside.
Drop garlic through feed tube and let chop for 10 seconds and then add cornstarch, salt, and pepper. While machine is still running, pour half-and-half through the processor feeding tube and blend for 15 seconds. Remove contents and transfer to a 3-quart saucepan, then stir in low-fat milk and herbes de Provence.
Cook contents in saucepan over medium heat, always stirring, for about 8-10 minutes, or as soon as the mixture begins to thicken. Once thick, stir in remaining cheese. Turn off heat, and set aside.
Cut a flat edge on each potato for easier use with processor. Switch to 45-mm slicing disc and then feed potatoes through feed tube, flat edge first, using medium pressure. Do this in batches, and once all have been sliced, set aside. Feed fennel bulbs through feed tube using medium pressure, and then set these aside as well.
Only using 1/3 of potatoes, arrange them at bottom of prepared baking dish as first layer. Next, using half of the fennel, arrange this in a second layer over the potatoes. Then pour 1/3 of the cheese mixture atop the fennel. Then use half of the remaining potatoes as the next layer, followed by the rest of the fennel, followed by a final top layer using the last 1/3 of potatoes. Pour the remaining 2/3 cheese mixture on top of tomatoes, making sure to fully submerge them. Sprinkle crumb mixture on top of all the layers.
Spray aluminum foil with cooking spray and then cover baking dish (coated side down). Bake in oven for 1 1/2 to 1 3/4 hours. Remove foil from potatoes and then cook for an additional 30 minutes. Let sit for 10 minutes outside oven before serving.