Lightly oil a 20cm x 30cm baking tin. Dust with icing sugar to coat, then set aside.
Pour the ale into a large bowl and whisk vigorously to get rid of most of the bubbles.
Tip half into a small non-stick pan and put the rest into the bowl of a free-standing mixer with the gelatine. Gently whisk to combine, then set aside.
Add the sugar, honey and ½ teaspoon of sea salt to the pan of ale. Place over a low heat, swirling the pan gently, for 10 to 15 minutes, or until the sugar has dissolved.
Turn up the heat to medium and bring the mixture to the boil. Pop your sugar thermometer in the pan and leave the syrup to gently boil for 10 minutes, or until it reaches 115ºC and is a light brown colour (don’t worry if the gelatine has set in the bowl, the hot sugar will re-melt it).
Take it off the heat and gently pour the mixture over the gelatine, with the mixer on a low speed.
Once all the syrup has been added, turn up the mixer to high and beat for 7 to 8 minutes, until fluffy.
In a separate bowl, whisk the egg whites with an electric whisk to stiff peaks, then fold them into the ale mixture, along with the vanilla, until combined.
Spoon the mixture into the prepared tin. Lightly grease a palette knife with oil and use it to smooth out the marshmallow mixture.
Dust with a thin layer of icing sugar and leave it to set at room temperature for 5 hours, or overnight.
When you are ready to finish off your marshmallows, place the chocolate in a heatproof bowl set over a pan of simmering water and melt it over a medium-low heat. Remove and set aside.
Pop the marshmallow block onto a chopping board and cut it into even-sized pieces. Using a toothpick, dip them in the chocolate and leave to set on a tray.
Crush and mix in the caramels with a pinch of sea salt. Just before the marshmallows have set, sprinkle some on top, leave to set fully at room temperature, then enjoy!