Preheat your oven to 350 °F (177 °C) and prepare a donut baking pan by spraying generously with non-stick spray.
In the bowl of a stand mixer equipped with a whisk attachment, combine the flour, sugar, baking soda, and salt. Whisk to combine.
In a large glass measuring cup, add the vegetable oil, buttermilk, egg, and vanilla and whisk until everything is well combined.
With the mixer on low speed, slowly pour the wet ingredients into the dry. Mix until just combined. Be sure to scrape the sides and bottom of the bowl to make sure all the ingredients are incorporated.
Add in ¼ cup finely chopped strawberries and fold until just combined.
Prepare a piping bag with a large round tip, or a large Ziplock bag with the corner removed. Add the batter to your bag being careful to not let the batter run out of the hole.
Pipe the batter into each donut mold, filling about ⅔ full.
Once you have all the batter piped, gently tap the tray against the counter 4-5 times to remove any air bubbles.
Bake for 13-15 minutes or until a toothpick inserted in the thickest part of the donut comes out clean.
Remove from the oven and allow to cool in the pan for 5 minutes before inverting onto a wire rack to cool completely.
Prepare the glaze by adding the powdered sugar and milk into a medium mixing bowl and whisk until smooth and there are no lumps.
Fold in the remaining ¼ cup chopped berries.
Once the donuts are cool, dip them, top side down, into the glaze and place face up on a wire rack to harden.
Serve and enjoy!
Notes
These are best served fresh, however, if you have any leftovers, place in an airtight container at room temperature for up to three days.I use Wilton piping bags, with a 2A piping tip for my donuts. Keep the tip pointed up until you are ready to pipe, or the batter will run through. You can also use a condiment bottle with a large nozzle/opening.