Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper or lightly grease them.
In a large bowl, whisk together the flour, powdered butter, granulated sugar, brown sugar, baking powder, and salt. Make sure the powdered butter is evenly distributed with no clumps. If you see any lumps, break them up with your fingers or sift the mixture.
In a separate bowl, whisk together the egg, milk, oil, and vanilla extract. If using powdered substitutes (egg powder or milk powder), make sure they're completely dissolved before proceeding.
Pour the wet ingredients into the dry ingredients. Using a wooden spoon or electric mixer on low speed, mix until a soft dough forms. The dough should hold together when pressed but not be sticky. If too dry, add milk one tablespoon at a time. If too wet, add flour one tablespoon at a time.
If making chocolate chip cookies, fold in the chocolate chips now. For other variations, add your mix-ins at this stage. Don't overmix – just fold until evenly distributed.
Using a spoon or small cookie scoop, drop rounded tablespoons of dough onto your prepared baking sheets, spacing them about 2 inches apart. The cookies will spread slightly during baking.
Bake for 12-15 minutes, until the edges are lightly golden but the centers still look slightly soft. Don't overbake – they'll continue cooking on the hot pan after removal.
Let cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely. They'll be soft when hot but will firm up as they cool to the perfect texture.