Is it possible to treat dairy with lactase to make it lactose free at home?
Ways to make lactose-free dairy at home

Grind your lactase pills into powder, dissolve them in warm water, and dump the solution into your milk. Wait 24-48 hours.
More convenient is to add 7 drops of liquid Lactase. Wait 24-48 hours and 70% of the lactose is gone.
More economical is to buy bulk lactase powder. Dissolve it in warm water and pour it into your milk. Wait 24-48 hours.
Another economical option is half-making yogurt. The yogurt bacteria (Lactobacillus bulgaricus, Streptococcus thermophilus, and Lactobacillus acidophilus) eat the lactose. I pour a gallon of milk into a pot inside another pot of water. Heat the milk to 185°F for 30 minutes. Then cool the pot of milk to 110° in cold water in the kitchen sink. Pitch the milk with 2-3 Tbsp. of plain fresh yogurt with &quot;active cultures&quot; and pour the milk back into the milk jug. Put the jug of milk into a food dehydrator (or anything else with good temperature control) and incubate at 104° for 3-4 hours. At that point you'll have slightly thickened milk. Shake it and use like normal. After 7 hours incubation you'll have yogurt. Strain off the whey and you'll have greek yogurt. Both have whey less lactose in them.

All these techniques will dramatically reduce the lactose in milk.
Fun Tips

Adjust the flavor of the milk-gurt by playing with the temperature. Lactobacillus bulgaricus prefers 110° and the other two prefer 99°. The different resulting acids (lactic, folic, formic) affect the flavor.
Yogurt bacteria break down lactose into acids. You can test the acidity to roughly determine how much lactose has been consumed.
The higher the acidity, the longer the treated milk will last.
You can mix-n-match, half-making yogurt and then adding lactase to the result.