Peel and chop the carrots into 1.5 cm chunks, and peel and cube the potatoes to match in size. Set aside.
Heat the oil in a large deep pan over medium heat until shimmering and fragrant. Add the chopped onion, and cook for about 5 minutes, stirring often, until it becomes translucent and slightly golden.
Add the ground cumin and turmeric to the onions, stirring quickly for about 30 seconds until the spices release their warm aroma.
Stir in the chopped carrots and potatoes, ensuring they are coated evenly with the spices. Cook for 3 minutes, allowing the vegetables to absorb the fragrant mixture.
Grate the fresh ginger and mince the garlic, then add them to the pan. Cook for about 1 minute until fragrant—listen for a gentle sizzle and smell the warm spices filling the air.
Pour in the coconut milk and water, stirring well to combine everything into a smooth, fragrant sauce. Bring the mixture to a gentle simmer.
Reduce the heat to low, cover loosely, and simmer gently for 20 minutes, stirring occasionally. The vegetables should become tender and the sauce slightly thickened, with a warm, inviting aroma.
Uncover and simmer for another 5 minutes, stirring to help the sauce thicken further. Taste and add salt or a squeeze of lemon to brighten the flavors.
Let the curry rest off the heat for a few minutes to allow the flavors to meld together, then serve hot over rice or with crusty bread. Garnish with fresh herbs if desired.