Preheat the oven to 350°F (175°C).

For a loaf cake, line a 9×5-inch loaf pan with parchment paper, leaving an overhang for easy lifting, and lightly grease the sides.

For a round cake, line the base of an 8-inch round pan with parchment and grease the sides.

In a large bowl, whisk together the flour, cocoa powder, sweetener (or sugar), baking powder, baking soda, and salt until well combined.

In a separate bowl, whisk the Greek yogurt, applesauce, eggs, oil, and vanilla extract until smooth.

Pour the wet mixture into the dry ingredients and stir gently until most of the flour is combined. A few streaks are okay, don’t overmix.

Add the hot coffee (or water) and whisk just until the batter is smooth and pourable. The batter will be thin, that’s what gives the cake its moist texture.

Pour the batter into the prepared pan and smooth the top.

For a loaf: bake for 38–45 minutes.

For a round: bake for 25–30 minutes.

The cake is done when a toothpick inserted in the center comes out mostly clean with a few moist crumbs (no wet batter).

Let the cake cool in the pan for 10 minutes, then transfer to a wire rack and cool completely before glazing (about 45–60 minutes).

Melt the chocolate and oil in a microwave-safe bowl in 20-second intervals, stirring in between, until 90% melted. Then stir off-heat until fully smooth.

Alternatively, use a heatproof bowl set over a pot of simmering water.

Stir in the chopped hazelnuts and a pinch of flaky salt (optional). Let the glaze sit for 5 minutes so it thickens slightly.

Place the cooled loaf cake back into the clean loaf pan (optional, for neat edges), then pour the warm glaze on top and spread it evenly.

Let the glaze set at room temperature for 30–40 minutes (or 10–15 minutes in the fridge) until firm but still glossy.

Slice and serve:

Use a sharp knife and wipe it clean between cuts for a bakery-style finish.

For a round cake, cut into wedges. For a loaf cake, slice thick pieces.