Name: Opera Fudge
Ingredients: 3½ pounds sugar; 1 quart cream; ½ teaspoon cream of tartar; 1 teaspoon vanilla (optional); melted chocolate (optional); chopped nuts or chopped cherries and citron (optional)

Why it works: Vanilla and chocolate are a kitchen classic. They rank in the top 5% of all ingredient pairs, and cooks put them together in 10,020 recipes. Both carry sotolon, which smells curry, maple. The science ↓

Opera Fudge

Ingredients

3½ pounds sugar
1 quart cream
½ teaspoon cream of tartar
1 teaspoon vanilla (optional)
melted chocolate (optional)
chopped nuts or chopped cherries and citron (optional)

Directions

The book gives no oven temperature. The 238°F (114°C) in the steps was added when the recipe was transcribed, as a starting point.

Make the syrup

Combine sugar and cream in a kettle.
Set over high heat and stir until it begins to boil.
Add cream of tartar and insert a thermometer.
Stir gently and constantly until it reaches 238°F (114°C).
Pour the mixture onto a moistened slab, but do not scrape the kettle.
Let it cool completely.

Cream and shape

Once cool, cream or turn the mixture until it forms a hard ball.
Cover with a damp cloth for 30-40 minutes.
When it sweats enough, mold it as desired or slice it into squares.
For vanilla fudge, add 1 teaspoon of vanilla while creaming.
For chocolate fudge, knead melted chocolate into the mixture after removing the damp cloth.
For the remaining fudge, mix in chopped nuts or cherries and citron as desired.

Set and cut

Pat the chocolate fudge into a lined box.
Smooth it to ¾ inch thick.
Let it harden for several hours.
To remove, turn the box upside down and peel off the wax paper.
Cut into small squares.

Recipe from a historical cookbook (Internet Archive).

Transcribed from a scanned cookbook and modernised for today's kitchens. Where the book gave no heat or time, or said "a moderate oven", the temperatures and times here may be modern equivalents rather than the book's own figures.

Explore the science

The flavor team

The pairs that carry this dish. Each one is judged two ways: how much their aromas overlap, and how often cooks already put them together.

Vanilla + chocolatetop 5% of all pairs

Smell alikemoderate

Cooked together10,020 recipes

Shared aroma: sotolon (curry, maple).
Vanilla + nutstop 8% of all pairs

Smell alikemoderate

Cooked together638 recipes

Shared aroma: alpha-pinene (pine, turpentine).
Sugar + vanillatop 8% of all pairs

Smell alikelow

Cooked together35,032 recipes

Shared aroma: beta-damascenone (apple, rose).
Sugar + creamtop 9% of all pairs

Smell alikemoderate

Cooked together43,450 recipes

Shared aroma: 2,3-butanedione (butter, sweet).
Chocolate + nutstop 10% of all pairs

Smell alikemoderate

Cooked together440 recipes

Shared aroma: furaneol (caramel, strawberry).

Sugar and vanilla barely smell alike, yet cooks put them together in 35,032 recipes: they work on texture and structure more than aroma.

Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs

What each ingredient does

Sugar: Provides the sweetness and the crystal structure that sets the fudge.
Cream: Adds fat and moisture, giving the fudge a smooth, rich texture.
Cream of tartar: Acidity that helps prevent large sugar crystals, keeping the fudge smooth.

The step that matters

Stir gently and constantly until it reaches 238°F (114°C). Sugar syrup must reach the right concentration to set into fudge. Stirring keeps the sugar dissolved and prevents crystals from forming unevenly, while stopping short or overheating changes the final texture.

“What each ingredient does” and “The step that matters” were written by Claude from this recipe’s own method and reviewed in samples by CompKitchen.