Preheat the oven to 350°. Place cake mix, buttermilk, egg, and vegetable in a large bowl and whisk until combined. There will be lumps left in the batter. (Do not over mix)
Place batter into a gallon sized ziploc bag and cut the corner off to create a 1-inch hole. Pipe batter into greased donut slots about half full. Bake for 10-12 minutes, or until edges begin to brown. Allow donuts to cool completely and carefully remove from the pan.
Prepare glaze by combing powdered sugar, melted butter, milk, strawberry extract, and food coloring with a spoon. To achieve the look of the donuts pictured (thick glaze and can't see the donut), spoon glaze over each donut and place on a wire rack to cool. For a thinner glaze (can see through glaze to the donuts), add more milk and dip donuts into the glaze halfway. Make the glaze as thick or thin as you want it by adding more or less milk. Immediately add sprinkles, if using.