Preheat the oven to 350°F (175°C). Thoroughly spray a 9-inch round pie dish (at least 2 inches deep) with cooking spray and set it on a baking sheet.
Add the 2 eggs, 1 cup granulated sugar, 3/4 cup milk or half-and-half, 1/2 cup Bisquick mix, and 2 teaspoons vanilla extract to the blender. Blend on high until smooth, about 15–30 seconds.
Add the softened cream cheese (cut into chunks) to the blender and blend on high until the batter is completely smooth, about 1–2 minutes depending on blender power.
Pour the batter into the prepared pie dish placed on the baking sheet and bake for 40–45 minutes, or until a knife or toothpick inserted in the center comes out clean or with a few moist crumbs but no liquid batter.
Remove the cheesecake from the oven and place it on a wire rack to cool completely; it will firm up and may fall slightly in the center.
In a medium bowl, whisk together 3/4 cup sour cream or Greek yogurt, 1/4 cup granulated sugar, and 1/2 teaspoon vanilla extract until smooth to make the glaze.
Evenly pour the glaze over the cooled cheesecake, keeping it toward the center and away from the raised crust edges. Sprinkle the chopped dark chocolate over the top.
Slice and serve, or cover with plastic wrap and refrigerate until ready to serve.