Bring 4 cups of water to a rolling boil in a 4-quart saucepan over medium-high heat.
Add the tea leaves and baking soda. Stand back a little — the water will foam up fast. Stir once.
When the foam reaches the top of the pot, pour in about half a cup of cold water. Let it roar back to a boil, then douse again. Repeat 3 to 5 times until the liquid is deep brick-red.
Take the pot off the heat and pour the red tea from high up — at least two feet — into a second pot or measuring cup. Pour it back, again from high, two or three times.
Set the pot back on medium heat. Pour in the whole milk and salt, stir once, and watch for a rosy bloom spreading from the edges toward the center.
Turn the heat to low and simmer gently for 10 to 12 minutes, stirring now and then, until the chai coats the back of a spoon.
Add the crushed cardamom pods, cover the pot, and steep off the heat for 5 minutes.
Strain into small cups, top with crushed pistachios and slivered almonds, and serve with sugar on the table.