Preheat oven to 350 degrees. In a bowl, using a fork, stir together all ingredients until well blended and batter begins to dry slightly (the more you stir the drier it will become, you just want it dry enough to be able to hold a shape and form a ball).: The oven warming creates a steady environment so the cookies bake evenly, producing slightly crisp edges while preserving a soft center. You should feel a gentle warmth when you open the oven and see a stable glowing rack, which means the heat is distributed. If the oven is not fully preheated your cookies may spread unevenly, or the center might stay too soft, so always wait until the temperature is steady.
Shape into a ball then transfer to a Silpat or parchment paper lined baking sheet.: The mixture will smell intensely of roasted peanut butter as the sugar incorporates, and the sound of the fork scraping the bowl is oddly satisfying. You want the dough to pull away from the sides slightly and feel tacky but not sticky. This drying is how the sugar and egg integrate with the peanut butter , giving the final cookie structure. A common mistake here is overmixing to the point of making the dough crumbly, so stop when the dough holds together without oozing.
Using the palm of your hand, flatten ball slightly, then using the fork gently press downward to make criss cross patterns over entire cookie (it should be about 3 1/2-inches across).: Rolling into a ball compresses the dough and creates surface tension, which helps even spread during baking. When you place the balls on the lined sheet you should hear a faint thud, and the surface will look smooth. Leave space between cookies because they will flatten a bit as they bake. Avoid packing the dough too tight, which can prevent even baking and produce dense centers.
Bake in preheated oven 12 - 15 minutes. Cool slightly then enjoy.: The pressing step creates the classic look and increases surface area, encouraging browned edges and a pleasing crisp. The fork marks also allow steam to escape, helping the whole cookie bake through without a gummy center. You should feel the dough give under the palm and hear a soft press; the fork marks should be visible but not cut through. Press lightly, because pressing too hard can make the cookies thin and brittle.
Bake in preheated oven 12 to 15 minutes: During baking the scent of toasted peanut butter will fill the kitchen and the edges will take on a light golden tone while the centers remain slightly pale. The small crackle around the fork marks signals doneness, and the cookie will firm as it cools on the tray. If you bake too long you risk drying them out, and if you remove them too early they may sink and be underdone, so aim for that faint golden edge and a slightly soft middle.
Cool slightly then enjoy: As the cookies rest, they finish setting and the internal steam redistributes, which firms the texture without making them hard. Place them on a wire rack if you can, and savor the warm aroma as they cool. A common mistake is handling them immediately off the tray, which can cause them to break, so give them a few minutes to settle before plating.