For the Caramel: Mix the brown sugar, cream, butter and salt in a saucepan over medium-low heat. Cook while whisking gently for 5 to 6 minutes, until it gets thicker.
Add the vanilla and cook another minute to thicken further.
Turn off the heat, cool slightly and pour into a jar or squeeze bottle. Refrigerate until cold. Stir it periodically to cool it down faster. Start the Syllabub once the caramel is chilled.
For the Syllabub: In a large mixer bowl, grate the lemon peel and juice the lemons.
Add sherry and sugar and whisk until sugar is dissolved.
Add the cream all at once and whisk until it forms medium peaks.
Gently fill your glasses half way with the Syllabub mixture. Top with a layer of caramel. Top with another layer of Syllabub mixture. Drizzle the top with caramel and top with some chopped peaches. Serve immediately.