Preheat and prep: Heat your oven to 350°F (175°C).
Line two baking sheets with parchment paper for easy release and even browning.
Cream the fats and sugars: In a large bowl, beat 1/2 cup softened unsalted butter, 1/2 cup sunflower butter, 1/2 cup light brown sugar, and 1/3 cup granulated sugar until fluffy, about 2 minutes. This traps air and sets you up for soft centers.
Add egg and vanilla: Beat in 1 large egg and 2 teaspoons vanilla extract until smooth. Scrape down the bowl so everything mixes evenly.
Whisk the dry ingredients: In a separate bowl, whisk 1 cup all-purpose flour, 1/2 teaspoon baking soda, 1/4 teaspoon baking powder, and 1/2 teaspoon fine salt.
Combine wet and dry: Add the dry ingredients to the wet and mix on low just until the flour disappears.
Don’t overmix or the cookies can turn tough.
Stir in oats and extras: Fold in 1 1/2 cups rolled oats. If using mix-ins, add up to 3/4 cup total. Chocolate chips and dried cranberries are a great combo.
Chill briefly: Cover and chill the dough for 20–30 minutes.
This helps the cookies hold their shape and bakes them thicker.
Scoop and space: Using a 1 1/2-tablespoon scoop, portion dough onto the prepared sheets, spacing 2 inches apart. For slightly thicker cookies, don’t flatten before baking.
Bake: Bake 9–12 minutes, until the edges are set and lightly golden but the centers still look soft. They’ll continue to set as they cool.
Cool: Let cookies rest on the sheet for 5 minutes, then transfer to a wire rack to cool completely.
If you like a hint of sweet-salty contrast, finish with a light sprinkle of flaky salt.