Whisk the dry ingredients: in a medium bowl combine 1.25 cups all-purpose flour, 0.5 cup unsweetened cocoa powder, 1 cup granulated sugar, 1 tsp baking powder, 0.5 tsp baking soda, and 0.5 tsp fine salt. Whisk to evenly distribute.

Combine wet ingredients: in a separate bowl whisk 1 large egg, 0.25 cup vegetable oil, 1 tsp vanilla extract, 0.5 cup milk, and 0.5 cup hot water until smooth. The hot water helps bloom the cocoa and thin the batter for a fudgy crumb.

Combine batter: pour the wet mixture into the dry ingredients and stir gently just until combined and no large streaks of flour remain. Do not overmix — a few small lumps are fine.

Bake: transfer batter to the prepared pan, smoothing the top. Bake for 22–28 minutes, or until a toothpick inserted near the center comes out with a few moist crumbs (not raw batter). The cake should be fudgy and slightly underbaked for best texture.

Cool: remove the cake from the oven and set on a wire rack. While still warm (5–10 minutes after removing), poke the surface several times with a skewer or fork to help the hot chocolate sauce seep in. Do not remove from pan yet.

Hot Chocolate Sauce (Fudge Topping)

Warm the dairy: in a small saucepan set over medium heat combine 0.75 cup heavy cream and 0.5 cup whole milk. Heat until it just begins to simmer around the edges—do not boil.

Add sugar and cocoa: whisk in 0.5 cup packed brown sugar and 0.25 cup unsweetened cocoa powder until dissolved and the mixture is smooth.

Melt chocolate: remove the pan from heat and add 4 oz chopped bittersweet or semisweet chocolate, 2 tbs unsalted butter, and 1 tbs light corn syrup. Let sit 1 minute, then whisk gently until the chocolate and butter are fully melted and the sauce is glossy.

Season and finish: stir in 0.25 tsp salt and 0.5 tsp vanilla extract. Taste and adjust: if you prefer a sweeter, thinner hot chocolate consistency, add up to 2 tbs more milk or a splash of hot water.

Infuse cake: while the cake is still warm with the poked holes, pour or spoon the hot chocolate sauce evenly over the surface. Use a spatula to coax sauce into any spots. Allow the sauce to sink in and set for 10–15 minutes; the cake will absorb some sauce and become deeply fudgy.

Finishing & Serving

Remove and slice: when the top sauce has set slightly but remains glossy (about 15–20 minutes after pouring), use the parchment overhang to lift the cake from the pan. Transfer to a cutting board and slice into 6–8 squares.

Serve hot or warm: for a pudding-drinks style presentation, place a square in a wide mug or bowl and pour 1 cup hot water (optional) over or alongside to create a drinkable hot chocolate with cake pieces, or simply serve on a plate.

Garnish: top each serving with whipped cream or marshmallows (about 0.5 cup divided), and sprinkle chocolate shavings or a dusting of cocoa powder (1 tsp) over the top.

Storage: store leftover cake in an airtight container in the refrigerator for up to 4 days. Reheat gently in a microwave (15–30 seconds per serving) and reheat extra sauce if needed to restore the hot chocolate puddle.