Preheat the oven to 350 degrees and line 12 muffin cups with paper liners.

In a double boiler, or very carefully in a microwave, melt the 12 ounces semisweet chocolate and butter together until very smooth.

Remove from the heat and let cool for a few minutes.

Mix in the sour cream, and stir until uniformly mixed.

In a large bowl beat the eggs one at a time until lemon colored.

Add the sugar and beat for three minutes. Beat in the melted chocolate mixture and the vanilla extract.

Add the sifted flour, soda, and salt to a sifter and sift the mixture into the chocolate mixture. Mix to barely moisten all of the ingredients.

Mix in 1 cup of the chocolate chips.

Pour the batter into the prepared muffin cups.

Sprinkle the remaining 1/2 cup chocolate chips over the tops.

Bake for about 20-25 minutes, or until the muffins are firm.

Remove the muffins from the tin and cool on a wire rack.

Once the muffins are cool to the touch, melt the white chocolate. Place the melted white chocolate in a frosting bag with a small tip, or use a condiment container or other container with a fine tip. Draw spider webs (or other shapes) on the cupcakes with the frosting. Let the chocolate cool and harden before serving or packaging.