Mashed Potato and Gruyère Grilled Cheese

Ingredients

• • 2 large slices country bread
  • 1 tbsp (15 ml) mayonnaise
  • 1 tsp (5 ml) whole-grain mustard
  • 1 tsp (5 ml) Dijon mustard
  • 3 oz (85 g) Gruyère cheese, thinly sliced
  • ⅓ cup (75 ml) mashed potatoes, hot (see note)
  • 1 tbsp fresh chives, finely chopped
  • Jalapeño pepper, seeded or not, thinly sliced, to taste
  • 1 tbsp butter