Mix the Ginger-Garlic Paste, coriander, turmeric, and 1/2 cup water in a small bowl. This is a simple wet masala (spice mix). Set aside.
In a large pot, warm the oil over medium-high heat until shimmering but not smoking. Add the serrano pepper, wait 30 seconds, and then add the cumin seeds and wait until they're done spluttering.
Add the wet masala (careful, it will also splutter). Cook until the paste thickens, deepens in color slightly, and oil oozes out of the perimeter of the masala, about 2 minutes.
Add the cauliflower and potatoes, stirring to coat the vegetables with the masala. Season with salt and add 1/2 cup water. Cover and cook over medium heat 10 to 15 minutes. Then, remove the lid, stir, and cook until the cauliflower and potatoes are cooked through, about 5 minutes. Garnish with cilantro and serve.
Throw the garlic, ginger, and canola oil in a mini-food processor and let it go until it forms a semi-smooth paste. There will still be tiny little pieces in there, but overall, it should resemble a paste.
Save what you don't use in a small glass jar. It should last in the fridge for 2 to 3 weeks. It's a delicious addition to marinades, pasta sauces, stir fry sauces, slow-cooker recipes, gravy etc. We always had a jar of this stuff in our fridge growing up.