Prep the oven and pan: Heat the oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone mats.
Soften the raisins: If your raisins are dry, soak them in warm water for 5 minutes, then drain and pat dry.
This keeps the cookies moist.
Mix the dry ingredients: In a large bowl, whisk oats, flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Stir in flax or chia if using.
Combine the wet ingredients: In a separate bowl or large measuring cup, whisk melted butter, oil, maple syrup (or honey), brown sugar (if using), egg, and vanilla until smooth.
Bring it together: Pour the wet mixture into the dry ingredients. Stir gently until no streaks of flour remain.
If the dough looks dry, add 1 tablespoon of milk at a time. The dough should be thick but scoopable.
Add the mix-ins: Fold in raisins and nuts (and chocolate chips if using). Avoid overmixing.
Portion the dough: Scoop heaping tablespoons (about 1 1/2 tablespoons each) onto the prepared sheets, spacing 2 inches apart.
Gently press each mound to about 1/2-inch thick for even baking.
Bake: Bake 9–12 minutes, rotating pans halfway. Pull them when the edges are set and lightly golden but the centers still look a touch soft. They firm up as they cool.
Cool: Let cookies rest on the sheet for 5 minutes, then transfer to a rack to cool completely.
This helps lock in their chewy texture.