In a large bowl, combine the pea or gram flour, chili flakes (if using), leeks, grated celeriac, garam masala, salt, baking powder and coriander leaves.
Using a spoon or your hands, slowly add the cup of water, mixing continuously. Give it a vigorous mix for a few seconds. You should have a thick creamy batter with air bubbles in it.
Heat the oil to a high heat. Test it is hot enough with a small amount of batter first - the batter should float and fry.
Place small handfuls of batter into oil at a time. Dropping these in should give a nice traditional pakora shape.
Fry the pakoras for 3-4 minutes until golden brown, turning half way through. Do not crowd the pan with pakoras, or they may turn out greasy.
Once cooked, place pakoras on a cooling rack with greaseproof paper underneath.
Serve with vegan raita. Mango chutney will also go really well with this.