Heat oven to 350ºF (180ºC). Spread nuts on a baking sheet. Roast, shaking occasionally, until golden inside, about 15 minutes. Let cool then wrap nuts in a kitchen towel and rub to remove the loose skins.
Make sugar syrup
Heat a sauté pan over med heat, add butter and melt. Add sugar and 2 tablespoons water and cook, stirring, until the sugar completely dissolves and the mixture turns a pale golden color, about 8 min.
Make hazelnut brittle
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. Chop the hazelnut mixture.
Add 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.
Add olive oil to a 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 until golden brown. 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.