In a heavy saucepan, combine 150 g sugar and 30 ml water. Cook over medium heat (without stirring) until it becomes a deep golden amber color (about 7–8 minutes).
150 g sugar, 30-60 ml water
Off the heat, carefully stir in 1 tsp espresso powder (or 15 ml brewed espresso). Be cautious, as it will bubble.
1 tsp instant espresso powder
Add 15–20 ml hot water to loosen the caramel, stirring until smooth.
15-20 ml hot water
Stir in 20 g butter until melted and smooth, then add 1/2 tsp flaky sea salt and mix well.
20 g unsalted butter, 1/2 tsp flaky sea salt
Quickly pour the coffee caramel into your 28 cm flan pan swirling to coat the bottom evenly. Set aside to cool slightly.