Prep the pan and oven. Preheat your oven to 350°F (175°C). Lightly grease a 6-cavity doughnut pan with nonstick spray or a thin layer of butter. This step keeps the doughnuts from sticking and helps them release cleanly.
Mix dry ingredients. In a medium bowl, whisk together 1 cup all-purpose flour, 1/3 cup granulated sugar, 1 1/2 teaspoons baking powder, 1/4 teaspoon salt, and 1/2 teaspoon ground cinnamon (if using). Whisk until there are no streaks and everything looks combined.
Combine wet ingredients. In a separate bowl or large measuring cup, whisk 1/2 cup milk, 1 large egg, 2 tablespoons melted unsalted butter (slightly cooled), and 1 teaspoon vanilla extract. The butter should be melted but not hot, so it doesn’t set on contact.
Make the batter. Pour the wet ingredients into the dry ingredients. Stir gently with a spatula or whisk just until combined. The batter should be smooth but not overmixed. A few small lumps are fine.
Fold in chocolate chips. Add 1/3 to 1/2 cup mini chocolate chips and fold them in. Mini chips distribute more evenly, so every bite has chocolate. If you only have regular chips, chop them a bit to avoid heavy pockets.
Fill the pan. Spoon the batter into the doughnut molds, filling each about 3/4 full. For a cleaner finish, transfer batter to a zip-top bag, snip the corner, and pipe it into the wells. Try to keep the center clear so the hole bakes through.
Bake. Place the pan on the center rack and bake for 10–12 minutes, or until the tops spring back lightly when touched and a toothpick comes out clean (melted chocolate on the toothpick is fine).
Cool and release. Let the doughnuts cool in the pan for 5 minutes, then run a thin spatula around the edges and lift them out to a wire rack. Cooling helps them firm up and prevents breaking.
Add toppings. Enjoy plain, or finish with one of the simple options below: Powdered sugar: Sift over warm doughnuts for a classic touch. Cinnamon sugar: Mix 1/4 cup sugar with 1/2 teaspoon cinnamon. Lightly brush doughnuts with melted butter and toss in the mixture. Vanilla glaze: Stir 1/2 cup powdered sugar with 1–2 teaspoons milk and a drop of vanilla until pourable. Dip the tops and let set. Chocolate drizzle: Melt 1/4 cup chocolate chips with 1 teaspoon oil in short microwave bursts. Drizzle over cooled doughnuts.
Serve. These are best slightly warm, when the chips are still a little melty and the crumb is soft.