The closest spread to peanut butter I've found in terms of flavor and texture is sunflower seed butter. It's also relatively easy to find; I've seen it in large chain grocery stores right next to the peanut butter.
A curmudgeon with years of practice. The bubbles in boiling water are steam or vaporized water. The bubbles initially do not reach the surface of the billing fluid as the colder water away from the hot bottom cools the steam turning it back to liquid. WHen all the water is at 100oC the bubbles reach the top.
This can end up heating the water faster than it can turn into vapor, causing it to become superheated. Bubbles of water vapor can then quickly form when the water is jostled as the cup is taken out of the microwave. This makes it boil up, seeming to explode, as all the vapor is suddenly released. But in reality, the conditions that make this happen are relatively rare.