Preheat the oven to 350°F (177°C). Line two baking sheets with parchment paper and set aside.
Sift the flour, baking soda and salt together in a bowl, and set aside.
In a large bowl, add room temperature butter and granulated sugar and beat on medium for about 3 minutes. Make sure to scrape the sides of the bowl in between mixing to get all the ingredients incorporated. After 3 minutes of beating, butter and sugar will become fluffy and lighter in color.
Add the egg and vanilla extract, mix until incorporated.
Add in the dry ingredients, mix on low until the flour is just combined. It's ok if you still see traces of flour left, we'll fold those in with raisins later on.
Fold in the raisins with a wooden spoon or a spatula.
With a cookie scoop or a spoon, scoop the cookies on the parchment paper, making sure to leave enough room between the cookies because they spread while baking. Gently press down on cookies just a bit so they spread more and you get a thinner cookie. If you like them more fluffy you can skip this part.
Sprinkle the tops with powdered sugar.
Bake in the preheated oven for 6 minutes, take them out and tap the cookie sheet on the counter a couple of times, then rotate the sheet and bake 4-6 more minutes, until the edges are golden brown.
Let the cookies cool down completely before transferring them to your container.