How hot should my water be? The hot water in this cake batter should be not quite boiling (175° F or so - about the temperature you’d use for making tea). You can bring water to a boil in a pan or kettle on the stovetop while you prepare the rest of your ingredients, or use an electric tea kettle to heat the water. If you don’t have the time or equipment to heat water this way, you can use water straight from the tap on its hottest setting - it won’t draw out quite as much chocolate flavor, but it will still work! The hot water in this recipe ensures our ingredients are mixed evenly, enhances the chocolate flavor of these cupcakes, and helps the cupcakes retain moisture as they bake.

Please use a kitchen scale! Measuring ingredients by volume (with cups) is notoriously unreliable: For best results, use a kitchen scale and measure your ingredients by weight using the gram measurements above. If you don’t have a scale, measure your ingredients (particularly flour and cocoa) with the scoop-and-level method for best results. 

Additions and Substitutions. Substitute melted coconut oil, olive oil, vegetable oil, or canola oil for the melted butter in the cupcake batter. You can also substitute melted coconut oil for the butter in the frosting if you like. Use white vinegar (preferred) or lemon juice in place of apple cider vinegar if you need to. If you’re running low on white sugar, you can replace up to 45 grams of white sugar with brown sugar. Use an egg white instead of an egg yolk if you prefer (the cupcakes won’t be quite as rich or moist as they are with an egg yolk, but they’ll still taste great!) Substitute your favorite frosting for the chocolate fudge frosting here - this recipe is great with chocolate or vanilla buttercream, peanut butter frosting, and cream cheese frosting!

The chocolate fudge frosting in this recipe will start to seize up as the butter cools, so work quickly to frost your cupcakes. The frosting will be quite thick and will resemble warm fudge - it won’t look or feel like the traditional buttercream or whipped frostings we’re often used to. If the frosting is too thin (this often happens when too much hot water is added) add extra powdered sugar or let it cool on the counter for a few minutes to thicken it up. If frosting is too thick, zap it in the microwave in 5-second intervals to loosen it. I love that this frosting develops a rich, fudge-like texture as it cools (it’s one of my most-requested frostings from friends and family!) but you could also absolutely use a more traditional buttercream here if you prefer.

If you use reusable silicone cupcake liners, you may need to extend the bake time by 1-3 minutes, and the cupcakes may not be quite as soft as they are with paper liners (but they’ll still taste good!) 

Storing and freezing. Extra cupcakes will last up to 5 days in an airtight container on the counter, although the texture is best if eaten within 1-2 days of baking. Freeze leftover cupcakes in an airtight container in the freezer for up to 3 months; defrost frozen cupcakes on the counter when you’re ready to eat them.