Ingredients
Equipment
Method
- Melt 2 tablespoons (28g) unsalted butter in a small bowl in the microwave in 15-second bursts until fully liquid, then set aside and cool for 2–3 minutes until warm but not hot.
- Add 1 large egg yolk (room temperature) and ½ teaspoon (2ml) pure vanilla extract to the cooled melted butter and whisk together with a fork for approximately 20 strokes until smooth, uniform, and no yolk streaks remain.
- Add 3 tablespoons (45ml) whole milk, room temperature, to the butter and egg yolk mixture and stir with a fork for 10 strokes until fully combined and no fat separation is visible.
- Pour the wet ingredient mixture into your 11–12oz (325–355ml) ceramic mug, then add 4 tablespoons (30g) all-purpose flour spooned and leveled, 3 tablespoons (18g) Dutch-process cocoa powder sifted, 3 tablespoons (36g) granulated sugar, and ¼ teaspoon (1g) baking powder directly on top of the wet ingredients.
- Using a fork, fold the dry ingredients into the wet from the bottom of the mug upward in approximately 25–30 strokes until no dry flour or cocoa streaks remain — fold, do not stir in circles.
- Add 1 tablespoon (approximately 10g) semi-sweet chocolate chips to the batter and fold in with 5–6 slow strokes until distributed; confirm the batter fills the mug no more than halfway.
- Place the mug in the center of the microwave turntable and microwave on full power for 60 seconds, then stop and assess — edges should look set and matte with the center still slightly wet and jiggly; if needed, microwave in 10-second increments only until edges are firm and center is just barely set on the surface.
- Immediately after removing from the microwave, scatter remaining 1 tablespoon (approximately 10g) semi-sweet chocolate chips across the hot domed surface, pressing each one lightly so the residual heat partially melts the bases and anchors them in place.
- Allow the cake to rest for 60 seconds, then drizzle 1 tablespoon (20g) chocolate sauce or warmed ganache across the surface in a back-and-forth motion allowing it to drip over the mug edges, then immediately finish with 1 pinch of flaked sea salt scattered across the warm sauced surface.
- Serve immediately in the mug while the center is still molten — the liquid center begins to set as the cake cools.
Notes
- Cocoa: Dutch-process only — not natural cocoa; natural cocoa changes color, lift, and leavening balance.
- Egg: yolk only, not whole egg — a whole egg sets the center completely and eliminates the molten interior.
- Mug size: 11–12oz (325–355ml) ceramic minimum — smaller mugs overflow; fill batter no more than halfway.
- Milk: whole milk only, room temperature — low-fat or plant-based milk changes moisture balance and center set time.
- Butter: unsalted, melted and cooled 2–3 minutes — hot butter partially cooks the egg yolk and breaks the batter.
- Vanilla: pure vanilla extract only — imitation vanilla has a sharper, artificial aftertaste that is more noticeable in small-batch recipes.
- Microwave wattage: tested at 1000 watts — add 15–20 seconds at 700 watts, subtract 10 seconds at 1200 watts.
- Storage: eat immediately; molten center sets within 20–30 minutes of baking — no true make-ahead version.
- Dry mix ahead: pre-mix dry ingredients and store in a sealed jar up to 1 month at room temperature.
- Scaling: make two separate mugs — doubling batter into one mug overflows regardless of mug size.
- Altitude: above 3,500 feet, reduce baking powder to ⅛ teaspoon and reduce cook time by 5–10 seconds.
- Allergens: contains gluten (flour), dairy (butter, milk), egg — chocolate chips may contain soy lecithin.
- Tip: pre-mix dry ingredients in a small bowl before adding to the mug to reduce strokes needed and prevent cocoa lumps.