Steam or boil diced sweet potato until very tender. Drain if necessary and mash or puree until you have your desired consistency. Let cool, then place in a sealed container in the fridge until ready to use.
In a medium bowl, whisk together egg, 1 Tbsp (15 mL) sweet potato puree, grated Cheddar, and formula or breast milk until well combined.
Heat a small pan over medium heat. Pour egg and sweet potato mixture in and allow it to cook on one side, about 2 to 3 minutes.
Use a thin spatula to flip omelette over onto the other side. Continue to cook until set and egg is cooked through completely. If omelette breaks apart while flipping, do not worry as you will be chopping it into pieces anyway!
Transfer to a small plate, let cool slightly and chop into tiny pieces that your baby can manage.