Preheat oven to 350ºF (180ºC). Spread the nuts in an even single layer on a rimmed baking sheet and roast, shaking the pan occasionally, until golden inside (break open to check), about 15 minutes.
Let cool slightly then wrap the nuts in a kitchen towel and rub to remove the loose skins then set aside.
Heat a small sauté pan over medium heat, add the butter and allow to melt. Add the sugar and 2 tablespoons water and cook, stirring constantly, until the sugar completely dissolves and the mixture turns a pale golden color, about 8 minutes.
Add the nuts, rosemary and salt and stir to combine and completely coat the nuts. Spread in an even layer on a parchment paper-lined baking sheet and let cool completely, about 20 minutes.
Roughly chop the hazelnut mixture and set aside.
For the whipped ricotta:
Add the ricotta, olive oil and lemon juice to a food processor fitted with a blade attachment (or blender) and pulse until completely combined and smooth. Cover and refrigerate until ready to use.
For serving:
Add the olive oil to a shallow dish and dip one of the cut sides of each slice of bread in the olive oil, then arrange the slices, oil-side up on a baking sheet.
Broil them just until golden brown, about 1 minute. Rub each slice with the clove of garlic.
Arrange the toasts on a platter and spread ricotta over the top. Sprinkle with the hazelnuts then finish with a drizzle of the truffle honey and serve.