Preheat oven to 350°F. Line muffin pan with cupcake liners.

In a large bowl, combine flour, salt, baking powder, and cocoa powder.

Cream butter and sugar with an electric mixer on medium speed.

Melt chocolate chips in microwave for about 40 seconds. Stir and microwave in 20-second intervals until smooth. Add to butter-sugar mixture and mix well.

Add eggs and egg yolks one at a time, mixing after each addition.

Stir in oil, vanilla, and sour cream until combined.

Gradually add dry ingredients to wet mixture, mixing until just combined.

Fill cupcake liners about 3/4 full.

Bake for 23 to 25 minutes or until a toothpick inserted in the center comes out clean. Cool in pan for 15 minutes, then transfer to a wire rack to cool completely.

For frosting, beat butter until smooth. Add half and half and vanilla, mix well.

Gradually add powdered sugar and dark cocoa, beating until smooth.

Frost cooled cupcakes and drizzle with chocolate sauce if desired.