Preheat oven to 175°Celsius. Line baking tray with parchment paper.
Sift flour and keep it aside.
In a clean bowl, cream the butter, peanut butter, granulated sugar and brown sugar until creamy. Add the egg and continue beating until it is well incorporated.
Next, vanilla extract and beat for about 15 seconds, followed by the sifted flour.
Mix until it is just incorporated and then add the sprinkles. Give the dough a few seconds of machine mixing and continue by hand with a spatula to make sure the sprinkles are well incorporated.
Rest the dough for about 5 minutes so that it comes together.
To bake the cookies, take about 1 tablespoon of dough and shape into round balls. Place the balls onto a lined baking tray. Repeat the process bearing in mind not to place the cookies too close to one another as they will spread during baking (since the recipe uses self-raising flour).
Press the top of each cookie lightly with a fork to flatten them slightly (dip the fork into flour to prevent it from sticking to the cookies.
Bake the cookies for about 9 minutes at 175°Celsius. At this temperature and cooking time, you will get peanut butter cookies that are slightly crispy on the edges and soft in the center. For crunchy peanut butter cookies (crunchy inside and out, bake the cookies for an extra 2 minutes).
To cool the cookies, lift the parchment paper off the baking tray and place it on a wire rack. Let the cookies cool completely before removing them from the paper. The cookies tend to stick to the paper when they are still warm. Store cookies in an airtight container.