Whisk the egg yolks and sugar together in a bowl until pale yellow and a little fluffy, with well-defined bubbles forming on the surface. Transfer the mixture to a saucepan, then sprinkle in the polenta, letting it fall between your fingers while stirring it in with a wooden spoon.

Pour the milk into a saucepan and heat over medium heat to just below boiling. Transfer the milk to a heatproof measuring pitcher. Set the saucepan with the polenta-egg mixture over medium heat and slowly stream in 2 cups / 475 ml of the hot milk while whisking continuously. Once the milk is in, continue whisking for about 5 minutes, until the polenta is fully cooked. Gauge the consistency: It should be dense but smooth and easy 
to whisk. If it isn’t, whisk in as much additional hot milk as necessary to achieve the right texture.

Turn off the heat, transfer the polenta custard to a cold bowl, and set it aside to cool completely.

Position a rack in the lower third of the oven and a second one in the middle of the oven. Heat the oven to 375˚F / 190°C / gas mark 5.

Cut each pear into quarters, then remove the core and stem. Slice each quarter into 4 slices. Crumble the amaretti coarsely. Use three-fourths of them to dust the bottom of the tart shell.

Pour the polenta custard over the amaretti and level it with a dampened offset spatula or dinner knife. Arrange the pear slices over the custard in concentric circles, leaving an empty circle in the center. Mound the remaining amaretti in the center circle.

Place the tart on a sheet pan, loosely tent it with aluminum foil, and slide it onto the rack in the lower third of the oven. Set a timer for 30 minutes. When it goes off, remove the foil and move the tart to the middle rack.

Set the timer for an additional 15 minutes, at the end of which you will test if the tart is done by touching its center; it should softly bounce but not jiggle. If the center still gives a little too much, return the tart to the oven for another 5 to 10 minutes, until it passes the bouncy versus jiggly test.

Remove the tart from the sheet pan and leave it just until the pan is cool enough to handle comfortably. Lift the tart from the outer pan ring and slide it from the bottom circle onto a plate large enough to contain it within its rim. Serve at room temperature.