Preheat your oven to 350°F (175°C). Lightly grease a standard 6-cavity or 12-cavity donut pan with non-stick cooking spray or a little bit of melted butter to ensure the donuts release easily after baking.
In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, cocoa powder, baking powder, and salt. Ensure there are no large clumps of cocoa powder left in the mixture.
In a separate medium bowl, whisk the buttermilk, egg, melted butter, and vanilla extract until smooth. Stir in the red gel food coloring until you achieve a deep, vibrant red hue. Gel coloring is preferred as it provides a stronger color without thinning the batter.
Pour the wet ingredients into the dry ingredients. Use a spatula to gently fold the mixture together until just combined. Be careful not to overmix, as this can make the donuts tough and rubbery.
Spoon the batter into a piping bag or a large plastic bag with the corner snipped off. Pipe the batter into the prepared donut pan, filling each cavity about two-thirds of the way full. This helps the donuts maintain their shape without overflowing.
Bake for 10 to 12 minutes, or until a toothpick inserted into the thickest part comes out clean. Let the donuts cool in the pan for about 5 minutes, then transfer them to a wire rack to cool completely before glazing.
In a small bowl, beat the softened cream cheese until smooth. Gradually add the powdered sugar and milk, whisking until you have a thick but pourable glaze. If it is too thick, add a few more drops of milk.
Dip the top of each cooled donut into the cream cheese glaze. Place a pair of plastic vampire teeth into the center hole of each donut. Use a small spoon or a toothpick to drip the strawberry or raspberry jam around the “fangs” to look like dripping blood.