For Sauce:
Take dry chillies and cut the top open. Remove the seeds out of it.
You can just invert it and roll between your hands, the seeds just fall off.
Now take the chillies and add it to a sauce pan. Add 1 cup of water and bring it to boil. Simmer it for 5 mins.
By this time the chillies must have plumped up. Drain chillies. Reserve the water, you need that for grinding.
Take the chillies in a blender add the reserved water slowly and make them into a paste. Set aside till use.
Now heat oil in a sauce pan. Add in garlic and ginger. Fry it for couple of mins.
Now add in the chilli paste and mix well. Now add in ketchup, soya sauce, salt, sugar and pepper. Mix well.
Simmer this sauce for 5 to 8 mins.
Now the sauce is done. Cool this and store in a clean air tight container refrigerated.
For Schezwan Potatoes:
Take baby potatoes in a cooker, add salt and cover with water. Pressure cook for 3 whistle, simmer and cook for 5 mins.
Turn off the heat and let the pressure go all by itself. Open the cooker, drain it and cool this down. Now peel off the skin and set aside.
Now take the potatoes in a bowl and sprinkle cornflour over it. Now toss it well.
Heat oil in a kadai. Add in the potatoes and saute till golden. Now remove it to a plate.
Now in the same oil add in schezwan sauce and toss well. Add in some chopped capsicum and saute for 5 mins or so.
Add in potatoes and mix well.
Now take 1 tsp cornflour and mix with some water. Pour this into the potatoes and toss well.
Serve with pulav, fried rice, naan or anything.