01 - Preheat oven to 375°F. Grease a donut pan with butter or non-stick spray.
02 - In a large bowl, whisk together the all-purpose flour, granulated sugar, baking powder, and salt until evenly distributed.
03 - In a separate bowl, whisk together the milk, eggs, melted butter, and vanilla extract until smooth.
04 - Pour the wet mixture into the dry ingredients and fold gently until just combined. Be careful not to overmix, as this can make the donuts dense.
05 - Transfer the batter to the donut pan, filling each cavity about two-thirds full to allow room for rising.
06 - Bake for 13 to 15 minutes, or until a toothpick inserted into the center of a donut comes out clean. Let cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
07 - Using a hand mixer or stand mixer, beat the softened butter on medium speed until pale and creamy, about 2 minutes. Gradually add the powdered sugar, beating on low until incorporated, then increase speed and beat until light and fluffy.
08 - Add the strawberry puree, vanilla extract, salt, and pink food coloring if using. Beat until the frosting is smooth, creamy, and spreadable.
09 - Once the donuts have cooled completely, spread or pipe the strawberry buttercream frosting generously over the tops. Serve immediately or store in an airtight container.