Add the pancetta to a cold pan and bring to medium heat, stirring often until the fat renders and the meat is golden brown, about 10-12 minutes. Remove the pancetta from the pan with a slotted spoon. Pour some of the oil out leaving behind 3 tbsp.
Bring a pot of water to a boil when the pancetta is almost finished. Boil your pastina to al denteas directed on the box. Save a coffee mug full of pasta water.
Use the same pan as the pancetta. Lower the heat to medium-low. Add the garlic and saute for 1-2 minutes.
When the garlic becomes fragrant, stir in a ladleful of pasta water and the strained pastina. Stir until most of the pasta water is absorbed.
Remove the pan from the heat. Stir the freshly grated parmigiana into the warm pastina, one scoop at a time. If all the pasta water is absorbed, add another ladleful. Stir often to combine into a creamy pastina.
Notes
Place pancetta in the freezer for 5-10 minutes before cutting to make it easier to cut.
Always cook pancetta starting from a cold pan. This is the best way to render the fat and make the pancetta crispy without burning. The fat will start to cook at a lower temperature than the meat.
Remove the pan from the heat when you add parmigiana so that the cheese doesn't "pill" or stick to the pan. You can see more about "pilling" in my Spaghetti Carbonara Do's and Don'ts.