Begin by heating your oven to 350°F (175°C). Line your baking sheets with parchment or a non‑stick mat so the cookies don’t stick and cleanup is easier. This also ensures even baking and prevents burning.
In your large bowl, beat together the softened margarine, peanut butter, white sugar, brown sugar, egg, and vanilla until the mixture is light and fluffy. This creaming step is essential for soft texture later.
Stir the flour, baking soda, and salt into your wet mix until well combined. You want a coherent dough without overmixing, which can make cookies tough.
Once your dough comes together, chill it in the fridge for about 15 minutes. This helps prevent spreading and gives more flavorful, thicker cookies.
Roll chilled dough into walnut‑sized balls and place them about 2 inches apart on your baking sheet. Bake for about 7–10 minutes until the edges turn a light golden color — be careful not to overbake!
Let the cookies cool on a wire rack once baked. Cooling helps them set properly and stay soft inside while slightly crisp on the edges.