Preheat the oven to a moderate baking temperature and line a baking sheet. The oven should feel hot but not extreme.
In a bowl, mix the butter and sugar until smooth and creamy. The mixture should look pale and soft.
Add the eggs and stir until fully mixed. The batter should look thicker and glossy.
Stir in the flour, salt, and leavening until just combined. The dough should be thick, not runny.
Fold in the rolled oats and raisins. You should see oats and raisins evenly spread through the dough.
Scoop the dough into rounded mounds and place them on the baking sheet with space between each one. Do not flatten them.
Bake until the edges look set and lightly golden, while the centers still look soft.
Let the cookies rest on the pan for a few minutes, then move them to a rack to cool. They will firm up slightly as they cool.
