1. To make the caramel sauce: Combine sugar and 1/4 cup water in a medium-size, heavy saucepan over medium-high heat, stirring to dissolve the sugar. Add the lemon juice, and bring to a boil. Cook, without stirring, about 5 minutes, until syrup turns golden. (Be careful not to let it burn.)
2. Remove syrup from heat. Using a wooden spoon, stir in the butter until melted. Pour milk into a small microwave-safe bowl. Microwave on HIGH 30 seconds. Gradually stir milk into caramel until blended. (Caramel will begin to harden.)
3. Return caramel to mediumhigh heat, and cook, stirring often, 1 minute, until hardened caramel has dissolved. Remove from heat, and stir in vanilla and salt (makes about 3/4 cup sauce).
4. Top cake slices with fruit, and drizzle with warm sauce.
Quick tip: Make the caramel sauce ahead of time and store in the fridge for up to 5 days. Serve warm.