For Chocolate Sauce: Place the cocoa, water, sugar, and salt in a small saucepan. Whisk over medium-low heat until the mixture is thick and the cocoa is completely dissolved, about 3 minutes. Remove from heat and stir in the vanilla. Pour into a covered jar or container. Cool to room temperature, then cover and store in the refrigerator.

For Caramel Sauce: Add the sugar and water to a 3-quart heavy-bottomed saucepan; stir lightly so it forms a flat, even layer. Heat the pot over medium heat and cook until the sugar dissolves, becomes clear, and begins to bubble. Do not stir anymore—just let it bubble, swirl the pan occasionally, and brush the sides of the pan as needed to prevent crystallization. Continue cooking until the mixture thickens and turns a deep amber color. Carefully add the butter and whisk until completely melted. Remove from heat and slowly pour in the cream, whisking continuously. Whisk in the vanilla and salt. Set aside to cool in the pan for 10 minutes, then pour into a covered glass jar and let cool completely.

For Strawberry Sauce: Combine the strawberries, sugar, lemon juice, and vanilla in a medium saucepan and bring to a boil. Reduce heat to a low simmer until the strawberries are soft and the syrup is thickened and reduced by 1 ⅓ to 1 ½ in volume, about 15 minutes, stirring occasionally. Store in an airtight container and keep refrigerated.

For Classic Vanilla Sauce: In a saucepan, heat the milk over medium heat until it is just steaming. In a bowl, whisk the egg yolks with the sugar until pale and slightly thickened. Slowly pour a little hot milk into the yolks, whisking constantly. Pour everything back into the saucepan. Stir over low heat until the sauce thickens enough to coat the back of the spoon. Remove from heat and stir in the vanilla extract or vanilla seeds. Chill or serve warm.