Here are the step by step instructions from Grathio Labs.
Ingredients:Supplies and Tools:
Slice the Bread.
Slice a piece of bread horizontally so you get two thinner slices of bread. This is by far the hardest part of the whole process.
Make more than you think you'll need. Some might break and they make somewhat shrimpy cones. Also they're so delicious that you'll want to eat more.
Form the cones.
For each bread cone roll a piece of paper into a cone shape and secure it with two paper clips. (You could use tape too, but I'm not sure how safe it is to bake with tape.)
Carefully roll your piece of bread into a cone making sure there's a little bit of overlap. Pinching the bottom and along the seam will help it hold together. Slide the bread into the paper cone so the bread will hold its shape.
It's okay if there's a hole in the bottom or if there are some small gaps. We'll be filling those holes with peanut butter.
I don't toast the cones, I found it was easiest (and just as tasty) to simply dry them out similar to making croûtons or bread crumbs
Place them in the center rack of your oven and set the oven to 250°F (120°C). When the oven reaches temperature (or after 15 minutes) turn off the heat and let them sit half an hour or until the oven cools.
If the cones are still a little spongy you can do the process again (or do it longer the first time). The cooking time will vary depending on your oven and the weather.
If the bread has trouble holding its shape inside the paper cones you can make a reverse sandwich with the bread between two paper cones. You'll need to bake them a little longer since it's harder for the water to escape.
If you don't want to use your oven because it will make extra heat you can just leave them in a warm place over night (like the top of the refrigerator or in a gas oven with a pilot light) and then finishing them off with 10 seconds in the microwave. Though technically this isn't baking, it's making stale bread.
Apply peanut butter.
This layer will keep the bread from getting soggy so cover the entire inside of the cone with peanut butter. Be sure to sure you get some in the bottom and fill any holes so the melting ice cream doesn't leak.
Add ice cream