Fill in a large saucepan (that has a steamer attachment) with water approximately 1/3 full. Place the saucepan without the steamer over high heat and bring the water to a rapid boil.
Whilst the water is heating, prepare the vegetables. Peel and chop the sweet potatoes and carrots into large chunks. Make sure they're chopped roughly the same size so they steam evenly.
Once the water has boiled, reduce the heat from high to medium. Transfer the potatoes and carrot into the steamer and attach it over the saucepan and cover. Steam the vegetables for 15 minutes.
Drain the lentils into a colander and rinse under cold water a few times. Place the lentils into a small heatproof bowl and place it on top of the vegetables in the steamer. Cover and steam for a further 5 minutes. The potatoes and carrots should be extra soft and pierce through effortlessly when inserting a fork or a skewer. If not steam for a further 5 minutes.
Use a tea towel to remove the bowl with the lentils carefully from the steamer. Place the carrots and potatoes into the food processor bowl along with the lentils. Process the vegetables at medium-high speed until it's the consistency of thick mashed potatoes. Add in a few tablespoons of boiled water and continue to pulse until you reach the desired consistency for your little one. You may need more tablespoons of water for younger babies to loosen up the mixture further. Allow the lentils and vegetable mash to cool at room temperature before serving.
Notes
(NOTE 1) Lentils - For convenience, I used lentils from the tin. Some supermarkets offer organic and no-salt-added tinned lentils. These are better choices for babies, especially if they're between 8 to 18 months old.Storage - Allow the puree to cool completely, then spoon them into baby food safe containers. Cover and freeze for up to 3 months. See how I store and organise my homemade baby food A Third-Party Application calculated the calories and nutritional information. Please use this as an approximate guide only.Cooking measurements are in Australian standard spoon and cup measurements.