Roast both types of peppers and peel. Separate the red peppers for puree and marinate the heirloom peppers in olive oil and salt to taste.
Peel and slice the purple potatoes one eighth of an inch thick. Blanch the potatoes in small batches until done.
Whip goat cheese with mascarpone and heavy cream until fluffy.
Trim and clean leeks. In an oven-proof dish, place the leeks side by side in a pan, then cover with water and white wine.
Add butter and salt. Braise, covered, in the oven at 350 degrees F. until fork tender.
Puree red peppers and season to taste. Add 1 teaspoon gelatin to ½ C. of hot water and dissolve. Add pepper puree to gelatin water and set aside.
Spay or oil a ceramic terrine mold and line with enough plastic wrap that will fold over the terrine.
Layer the ingredients in thin layers in this order: potatoes, cheese, leeks, pepper puree, and peppers.
Fold more plastic wrap over the top. Cover and chill for at least a half-hour.
Bake the terrine for 40 minutes in a water bath at 250 degrees F. Cool, then refrigerate terrine overnight.
Slice and serve with herb salad and vinaigrette dressing.