- Preheat an oven to 350°F
- Quarter each tangerine and remove the peel from the flesh. Using a sharp thin knife, remove the white pith from the peel; discard the pith. Slice the peel lengthwise as thinly as possible. You should have about 3/4 cup peel.
- Using your fingers, separate the pulp from the membrane and place the pulp in a measuring cup; discard the membrane. You should have about 1 1/3 cups pulp.
- In a saucepan over medium-high heat, combine the peel, pulp, water and sugar and bring to a boil, stirring constantly. Boil, stirring occasionally, until the marmalade begins to thicken, 18 to 20 minutes. Transfer to a heatproof bowl and let cool. The recipe makes about 1 cup (10 oz./315 g) marmalade; you will need 1/3 cup (3 1/2 oz./105 g) for this recipe. Refrigerate the rest for up to 1 week.
- Line a baking sheet with parchment paper.
- Brush the baguette slices on both sides with the olive oil and season lightly with salt. Place on the prepared baking sheet. Bake, turning once halfway through, until the bread is golden brown and toasted, about 10 minutes. Let cool for 10 minutes.
- Spread 1 tsp. ricotta cheese on each crostini and top with a scant 1 tsp. marmalade, then garnish with a small pinch of mint.