Preheat the oven to 350°F (175°C). Grease a 9-inch round cake pan (or two 8-inch pans) with 1 tablespoon butter or nonstick spray, then lightly dust with 1 teaspoon cocoa or flour; tap out excess.

Combine dry ingredients

In a large bowl, sift or whisk together 1.75 cups all-purpose flour, 0.75 cups unsweetened cocoa powder, 1.75 cups granulated sugar, 1 teaspoon baking powder, 1 teaspoon baking soda, and 1/2 teaspoon fine salt until evenly combined.

Whisk wet ingredients

In a separate medium bowl, beat 2 large eggs lightly, then whisk in 1 cup whole milk, 1/2 cup neutral oil, and 2 teaspoons pure vanilla extract until homogenous.

Combine wet and dry

Pour the wet mixture into the dry ingredients and stir with a sturdy spatula or whisk until mostly combined and no large streaks remain. Do not overmix — a few small lumps are fine.

Add hot water

Slowly add 1/2 cup hot (but not boiling) water to the batter while gently stirring. The batter will be thin — this yields a moist chocolate crumb. Scrape the bowl and ensure ingredients are evenly distributed.

Bake

Pour the batter into the prepared pan, smoothing the top. Bake in the preheated oven until a toothpick inserted near the center comes out with a few moist crumbs, about 30–36 minutes for a 9-inch round (20–26 minutes for 8-inch pans). Rotate the pan halfway through baking for even color.

Cool

Remove the cake from the oven and let it cool in the pan for 10 minutes. Run a thin knife around the edge, invert onto a wire rack, peel off the parchment (if used), and let cool completely, about 1–1.5 hours. Chilling for 20–30 minutes makes cutting heart shapes cleaner.

Chocolate glaze & assembly

Prepare glaze

Place 6 oz finely chopped semi-sweet chocolate, 3 tablespoons unsalted butter, and 1/4 cup heavy cream in a heatproof bowl. Heat gently in 20–30 second bursts in the microwave, stirring between intervals, until the chocolate and butter have melted and the mixture is smooth. Alternatively, set the bowl over a simmering water bath and stir until smooth. If desired, whisk in 1 tablespoon powdered sugar for a slightly thicker, glossy finish and 1 teaspoon shortening or extra butter for added sheen.

Thin glaze if needed

If the glaze is too thick for pouring, warm it very briefly (5–10 seconds) or whisk in 1–2 teaspoons warm cream or hot water until it reaches a pourable ribbon-like consistency.

Cut heart shapes

When the cake is completely cool and slightly firm, use a 3–4 inch heart-shaped cookie cutter to cut hearts from the cake. Press straight down to make clean edges. If you used a heart-shaped pan, you can skip cutting and use the whole cake. Arrange the hearts on a wire rack set over a baking sheet to catch excess glaze.

Glaze the hearts

Place the wire rack with cake hearts over the baking sheet. Pour the warm chocolate glaze over each heart, starting at the center and letting it flow to the edges so the top and sides are coated. Use a small offset spatula to smooth and encourage even coverage. Let excess drip; return drips to the bowl to reuse if desired.

Set and finish

Allow glazed hearts to sit at room temperature until the glaze sets, about 20–30 minutes. For a quicker set, chill in the refrigerator for 10–15 minutes. Once set, dust lightly with 1 tablespoon confectioners' sugar or sifted cocoa powder for a simple, romantic finish.

Finishing & serving

Transfer the set heart chocolate cakes to a serving plate. Serve at room temperature for the best texture. Store any leftovers in an airtight container in the refrigerator for up to 4 days; bring to room temperature before serving for softer crumb (about 30 minutes).