Begin by arranging your oven racks so they sit in the upper and lower thirds, then preheat the oven to 350°F. Prepare two baking sheets by lining them with parchment paper to ensure the cookies bake evenly and don't stick.

In a medium-sized bowl, thoroughly whisk together the flour, oats, baking powder, baking soda, and salt. Set this dry mixture aside.

Using an electric mixer, cream the butter and brown sugar together on medium speed until the mixture becomes fluffy and light, approximately 3 minutes. Make sure to scrape down the sides of the bowl with a rubber spatula to ensure even mixing. Add the egg and vanilla extract, then beat again for about 30 seconds until the mixture is smooth and fully incorporated.

Gradually incorporate the dry ingredients into the wet mixture, mixing on low speed until just combined. Be cautious not to overwork the dough. Fold in the chopped pecans and raisins or currants gently, ensuring they are evenly distributed throughout the batter.

Scoop the dough into mounds measuring about 1½ tablespoons each and place them on the prepared baking sheets, spacing them 2 inches apart to allow for spreading. Bake the cookies for 11 to 13 minutes, rotating the sheets midway through to ensure uniform baking. The edges should appear lightly golden while the centers remain slightly pale.

Allow the cookies to cool directly on the baking sheets for a few minutes. You can then either slide the parchment paper onto cooling racks or carefully transfer the cookies using a spatula. Once fully cooled, store them in an airtight container to maintain their freshness and texture.