Line a flat sheet pan with a nonstick rubber mat. Place a .5-cm- / .25-in-deep stainless steel frame on the mat. The frame should fit just inside the pan.
Bring the milk, cinnamon, and lemon zest to a boil in a saucepan over medium-high heat.
Add the rice and stir constantly, making sure it doesn’t stick to the bottom of the pot. Turn the heat down to