1 cup flour
1/2 unsweetened cocoa powder (not Dutch process)
1 cup sugar
1/2 tsp. baking soda
1/4 tsp. salt
3/4 cup hot water
1/2 cup canola oil
1 large egg
1 1/2 tsp. vanilla extract
Heat oven to 375°F. Line 12 regular-sized muffin cups with paper or foil liners.
Combine flour, cocoa, sugar, baking soda, and salt in a blender. Cover with the lid and blend on medium speed until blended. Pour in the water, oil, egg, and vanilla. Cover with the lid and blend on medium-high speed until smooth and well blended, stopping to scrape down the sides once or twice. Pour into lined muffin cups, dividing evenly. Bake until a toothpick inserted in the center of one cupcake comes out clean, 17–19 minutes. Transfer to rack to cool for about 10 minutes, and then carefully remove the cupcakes from the pan and set them on the rack to cool completely before frosting.
For the frosting:
8 ounces bittersweet chocolate, finely chopped
8 tablespoons unsalted butter, cut into pieces
1 cup sweetened condensed milk (not evaporated)
1/4 cup light corn syrup
1 teaspoon vanilla extract
1 Pinch salt
Melt chocolate and butter in the microwave. Add condensed milk, corn syrup, vanilla and salt. Whisk until well blended. Set aside at room temperature, whisking frequently. It will thicken as it cools. When completely cool, cover with plastic wrap until ready to frost.