Place the quartered potatoes in a large pot and cover with cold, salted water.
Bring to a boil, then reduce the heat to a vigorous simmer.
Cook for about 20 minutes, or until very tender.
Drain thoroughly.
While the potatoes cook, melt 1 tablespoon (15 ml / 0.5 fl oz) of butter or heat the oil in a large skillet over medium heat.
Add the chopped asparagus and cook, stirring frequently, for 2-3 minutes until crisp-tender.
Stir in the peas and fresh herbs, season with salt and pepper, and cook for another 1-2 minutes until everything is heated through.
Transfer the vegetable mixture to a large mixing bowl.
Add the drained, hot potatoes to the bowl with the vegetables. Roughly mash everything together with a potato masher or fork, leaving some texture.
Taste and adjust the seasoning.
Let the mixture cool for a few minutes. If it seems too wet to hold its shape, stir in a tablespoon or two of flour.
Shape the mixture into 4 to 6 evenly sized patties. For best results, you can chill the patties for 30 minutes to help them firm up.
Wipe out the skillet and add 2 tablespoons (30 ml / 1 fl oz) of the remaining butter or oil over medium heat.
Once hot, carefully place the burgers in the pan.
Cook for about 5 minutes per side, until golden brown and crisp.
Add more butter or oil if the pan becomes dry.
Serve immediately on buns with your favorite toppings, or on a plate with a side salad.
Don't over-mash the potatoes! Leaving some larger chunks creates a more interesting and rustic texture in the final burger.
