In the bowl of a stand mixer fitted with the dough hook attachment, combine all of the dough ingredients and knead on medium low speed for about 5 minutes. The dough should come together in a cohesive ball that pulls away from the sides of the bowl but is still slightly sticky. If the dough does not come together, add in more flour 1 tablespoon at a time until the dough pulls away from the sides of the bowl.
Place the dough in a large, lightly greased bowl and cover. Place the dough in the fridge and chill overnight (8-12 hours).
In the morning, remove the dough from the fridge and allow it to rise at room temperature for about 30 minutes.
When the dough is finished rising, lightly punch it down and then turn it out onto a lightly floured surface. Roll the dough into a large rectangle about ½ inch thick.
Using a 3 inch heart shaped cookie cutter, cut out the heart donuts. Then using a smaller heart, cut out the center. (I like to leave some whole to fill with jam). Re-roll the scraps one time to get more donuts. Then if you have any leftover scraps, you can make extra donut holes! Lightly cover the donuts and let rest while the oil is heating.
Pour 2-4 cups of vegetable oil (you want it to be about 2 inches deep) into a large, heavy bottomed pot or dutch oven and heat over medium high heat until the oil reached 375°F. Place a cooling rack on top of a baking sheet and position it next to your stove. [I love this thermometer because it clips to the pot.]
Once the oil reaches 375°F, fry 3-4 donuts at a time for 1 minute on each side. The donuts should be a deep golden brown. Remove from the oil and place on the cooling rack to allow excess oil to drain off. I always make 1 donut first and check to make sure it's cooked through!
Repeat with the remaining donuts as well as the donut holes.
For the solid heart donuts: While they're still warm, toss them in a little granulated sugar! Place back on the cooling rack and allow to mostly cool to room temperature before filling. Add your favorite strawberry jam to a piping bag fitted with a large bismark tip. Poke the bismark tip into the top of each donut and fill with the jam. [It's easiest to make a hole in the top of the donut using a chopstick prior to filling.]
For the standard heart donuts: In a small bowl, whisk together the powdered sugar, melted butter, and vanilla. Slowly mix in the milk until your desired consistency is reached. The glaze should be thick but still pourable. If desired, add in a couple drops of pink food coloring. Dip the heart donuts into the glaze and place back on the cooling rack so the excess can drip off. Sprinkle with the Valentine's sprinkles immediately after glazing, so that they stick.
Notes
Please note that this recipe was specifically designed for deep frying the donuts. If you would prefer baked donuts, I suggest looking up a different recipe.These donuts are best eaten the same day, but will keep covered in the fridge for up to 2 days. They taste best re-heated in the microwave for 10-20 seconds.