Heat oil in a large pot and sauté the veggies for about 10 minutes on medium-low heat.
Add salt and chopped parsley and mix. Continue cooking for 10 more minutes, stirring occasionally.
Take it off heat and allow it to cool down slightly. Use a stick blender to blitz the mixture until it is a slightly chunky paste.
Transfer the paste to a parchment paper lined glass container. Cover with a lid and freeze for about 5 hours.
Remove from the freezer and let it sit out for a couple of minutes. Use a sharp knife to cut the mixture into cubes.
Wrap the individual cubes in parchment paper or wrapping paper.
Transfer to an airtight glass jar and freeze until you're ready to use.
Notes
Taste and add more seasonings, herbs and spices to amp up the flavor of these veggie stock cubes if you want to. Spices like black peppercorns, bay leaves and chilies and veggies like parsnips and bell peppers can be great additions to this.
For extra depth of flavor and a bright color, add a couple of teaspoons of tomato paste into the mix, towards the end.
Dried herbs and spices like dehydrated jalapenos, garlic powder, onion powder and ginger powder can also be added to this. Play around with the flavors and taste as you go. Remember that the mixture is supposed to have that concentrated flavor.
Remember that due to the high salt content, these cubes won't be completely solid. Don't be alarmed if they seem just a bit softer than your regular store-bought bouillon cubes.
I used butter instead of oil as the base while making my gluten free Japanese curry roux, and if you're not sensitive to dairy, you can do that too.