Preheat oven to 250 & line baking tray with parchment paper.
Mix well the following ingredients with a hand-mixer: peanut butter, butter, brown sugar & vanilla
Add in the egg & mix until just blended
Sift the following ingredients separately: flour, baking soda & salt.
Then, add into the other mixture slowly to blend in properly.
Scoop out the final mixture with a tablespoon & roll into a ball roughly (doesn't have to be super perfectly round) to arrange row by row on the baking tray.
Use a fork to press down flat slightly twice in different directions to shape a classic crisscross.
Bake for about 8 - 10 mins.
Then, bring tray out from oven to let it cool for about 2 mins & transfer to the cooling tray after that.