Preheat your oven to 400°F.
Trim the green tops off your strawberries, then place them in a food processor. Pulse until you have a chunky puree.
In a large mixing bowl, combine unsalted butter, sugar, and egg. Mix on medium-high speed for about 2 minutes until creamy.
Add in your vanilla extract, buttermilk, and strawberry puree into the mixture. Blend until everything is combined smoothly.
Add both flours along with baking soda, baking powder, and salt to the wet mixture. Mix on low speed until just incorporated.
Transfer your donut batter into a piping bag or freezer bag for easier filling of the donut tin. Grease each mold generously before filling.