Get Ready: Start by preheating your oven to a cozy 400°F (200°C). Grab a 12-well donut pan and give each well a light spray with nonstick cooking spray. Set it aside for now.
Whip Up the Batter: In a big mixing bowl (or using your stand mixer with a paddle attachment), combine the Bisquick baking mix, granulated sugar, sour cream, milk, egg, vegetable oil, and vanilla extract. Mix everything on low speed until it just starts to come together, then scrape down the sides of the bowl. Increase to medium speed and mix until your batter is smooth and lump-free. Be careful not to overmix!
Fill 'Em Up: Gently spoon the batter into each prepared donut pan well, filling each one about two-thirds full. This helps create that perfect donut shape with a nice clear hole in the middle.
Bake to Golden Perfection: Pop the donut pan into your preheated oven and bake for about 9 to 12 minutes. You'll know they're ready when a toothpick inserted into the center of a donut comes out clean and the donuts spring back lightly when you touch them.
Cool Down: Take the pan out of the oven and let the donuts cool right there in the pan for about 5 minutes. After that, carefully flip them out onto a wire rack to cool completely. If you're adding toppings, make sure the smoothest side is facing up!
Optional Toppings for Extra Fun:
Cinnamon Sugar Delight: While the donuts are still warm, dip the smooth top surface of each donut into the melted butter, then immediately into a separate shallow dish where you've mixed the sugar and cinnamon. Place them back on the wire rack.
Silky Chocolate Glaze: Once the donuts are completely cooled, put the chocolate chips, butter, and milk into a small microwave-safe bowl. Microwave for 30 seconds, stir well, then microwave for another 15 seconds if needed, until everything is smoothly melted. Whisk in the sifted powdered sugar until your glaze is silky and smooth. Dip the top of each donut into the chocolate glaze, then return them to the wire rack (chocolate side up). If you like, sprinkle with sprinkles while the glaze is still wet. Let the donuts sit for about 15 minutes to allow the glaze to set to a lovely satiny finish.
Enjoy! Serve your wonderful homemade baked donuts warm or at room temperature.