Melt together the butter and water/milk until the butter is just melted and the milk isn't too hot (it will kill yeast if it's too hot for you to hold your finger in).
In a stand mixer with dough hooks, mix salt, sugar, yeast, and 2 ½ cups flour.
Add in milk/butter to flour mix and beat on medium speed for 2 minutes.
Add in 1 ½ cups flour, and knead until well combined. You want the dough to pull away from the sides of the bowl, NOT stick to it, and be "soft as a baby's bottom." If it's not there yet, add in flour a couple tablespoons at a time.
Once it's the right consistency, let machine knead for 3-5 minutes until bread hits windowpane stage.
Cover mixer bowl and let rise until doubled, about an hour.
Get your loaf pans ready - I prefer to line with parchment vs greasing and flouring. It's less work for me. I prefer a smaller sized loaf pan for tall loaves, but two 8"x4" pans work well.
When doubled, dump dough onto a lightly floured counter, divide in two, and shape your loaves.
Put your bread pans inside of a plastic bag. I reuse a turkey roaster bag for this but you can even use a grocery bag. Make sure it's inflated with air and tie it off so it stays blown up like a balloon. This creates an excellent "proofing chamber" for your bread to rise well.
Look at how your dough is now, maybe "measure" how tall up the pan the dough is with your fingers like you were measuring 2 fingers of whiskey. For me, it was 3 fingers. This helps me so I can know when the bread is doubled. Letting your bread truly fully double before baking is the trick to this bread being as light and fluffy as can be. It takes about 30-60 min depending on your house temperature.
Before the dough is quite doubled, preheat the oven to 350F, with the rack in the middle. NOT CONVECTION. Convection setting actually inhibits your bread from springing up well when baked!
When dough is sufficiently doubled, slide into the oven and set timer for 20 minutes. After 20 minutes, turn pans around. Bake another 5-10 minutes more. (If your oven runs hot, check after 5 minutes.)
Because ovens vary, I always suggest taking your bread's internal temperature with an instant read thermometer. It should be over 180F, usually in the area of 190F. If its over 180F you're good, it will continue to rise a bit after you take it out of the oven.
When the internal temperature is right, take it out of the oven, leave the loaves in the pans, and set a timer for 10 minutes. When the timer goes off, take the bread out of the pans. This 10 minute rest helps the sides and bottom of the loaves stay softer.
If you really want to do this right, take a stick of butter and rub it all over the tops of the bread while it's still warm for the ultimate soft top crust.
If you plan to eat the whole loaf in one sitting, you can cut into it while it's still hot. Otherwise let it sit at least an hour, ideally until room temp, until you cut into it. The "crumb" of the bread is still setting up and if you cut into it, it releases the steam that's doing so, and causes your bread to get a bit gummier as it cools.
Store in a container on bag on the counter. Stays cold sandwich worthy for a good 3 days in our 20C/70F house.