1. Prepare the Pink Heart Sponge:

• Preheat your oven to 180°C (160°C fan) or 350°F. Grease and line a 2lb loaf tin.
• In a mixing bowl, cream together the softened butter and caster sugar until light and fluffy.
• Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next.
• Mix in the vanilla extract.
• Gradually fold in the self-raising flour until the batter is smooth.
• Add enough pink gel food coloring to achieve a vibrant shade, mixing thoroughly.
• Pour the batter into the prepared loaf tin and bake for approximately 50 minutes, or until a skewer inserted into the center comes out clean.
• Once baked, allow the cake to cool in the tin for a few minutes before transferring it to a wire rack to cool completely.

2. Create the Heart Shapes:

• Once the pink sponge has cooled, slice it into pieces approximately 2cm (¾ inch) thick.
• Using a small heart-shaped cookie cutter, cut out heart shapes from each slice. Set these hearts aside.

3. Prepare the Chocolate Loaf Batter:

• Preheat the oven again to 180°C (160°C fan) or 350°F. Grease and line the loaf tin once more.
• In a mixing bowl, cream together the softened butter and caster sugar until light and fluffy.
• Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next.
• Mix in the milk.
• Sift in the self-raising flour, cocoa powder, and baking powder. Fold gently until the batter is smooth.

4. Assemble the Cake:

• Spoon a thin layer of the chocolate batter into the bottom of the prepared loaf tin.
• Arrange the pink heart cut-outs in a straight line along the center of the tin, ensuring they fit snugly together.
• Carefully spoon the remaining chocolate batter over the hearts, ensuring they are fully covered. Smooth the top with a spatula.
• Bake for approximately 50 minutes, or until a skewer inserted into the cake (avoiding the center where the hearts are) comes out clean.
• Allow the cake to cool in the tin for a few minutes before transferring it to a wire rack to cool completely.

5. Prepare the Chocolate Buttercream:

• In a mixing bowl, beat the softened butter until creamy.
• Gradually add the icing sugar, mixing well after each addition.
• Pour in the melted and cooled dark chocolate, vanilla extract, and 1 tablespoon of milk. Beat until the buttercream is smooth and fluffy. If the mixture is too stiff, add an additional tablespoon of milk.

6. Decorate the Cake:

• Once the cake has cooled completely, spread or pipe the chocolate buttercream over the top.
• Decorate with heart-shaped sprinkles if desired.
• Slice to reveal the hidden heart surprise inside.