Fry onion, garlic, and ginger in oil until onion becomes translucent.
Add turmeric, cumin, coriander seeds, and mustard seeds, and stir for 1 minute until content become aromatic but before burning.
Add beetroot, stock powder, chilli, and enough water to cover it. Cook on medium heat for 20 minutes, stirring occasionally to make sure it doesn't catch on the bottom of the pan.
Add sweet potato, coconut milk, lemon juice, and curry leaves. Cook for a further 10 minutes or until sweet potato is tender.
Add garam masala, check the seasoning.
Serve with rice.

1 brown onion, finely chopped
2 garlic cloves, minced
2cm knob of ginger, minced
2 teaspoon vegetable oil
4 medium beetroots, cut into 2cm cubes
1 medium sweet potato, cut into 2cm cubes
1 green chilli, de-seeded and minced
1 teaspoon stock powder
1 tablespoon turmeric
2 teaspoon ground cumin
2 teaspoon ground coriander seeds
2 teaspoon whole brown mustard seeds
3/4 cup coconut milk
juice of 1 lemon
2 tablespoon curry leaves
2 tablespoon garam masala