Pop the broad beans out of their pods. Drop into a pan of boiling water. Simmer for 2 mins. Lift them out with a slotted spoon and plunge into ice water. Drop the sugar snap peas into the boiling water (keep them whole as you can eat the pods). Cook for 1 min. Drain. Plunge them into a separate bowl of iced water.
Peel and finely chop the red onion. Peel and crush the garlic. Pop the onion and garlic into a jam jar. Add 1 tbsp honey, 2 tbsp vinegar and 2 tsp black onion seeds with 1 tbsp olive oil. Season. Screw on the lid and shake.
Pop the broad beans from their grey skins. Drain the sugar snap peas and pat dry with kitchen paper. Lay on a large serving platter. Scatter over the broad beans.
Thinly slice the chilli. Heat a frying pan. When hot, pour in 2 tbsp oil. Tip in 2 tsp mustard seeds and 1 tsp coriander seeds. Fry them for about 2 mins till they pop. Remove from the heat and stir through the chilli.
Toss the beans and peas through the pink onion dressing. Spoon over the popping hot oil. Scatter over the tarragon leaves and serve immediately.