Special equipment: 2 pieces cheesecloth (for homemade ricotta)
Preheat the oven to 450 degrees F.
Combine the grapes, honey and 1 tablespoon of the olive oil in a bowl and mix to coat the grapes. Place the coated grapes on a rimmed baking sheet and add the thyme sprigs, salt and pepper. Roast until the grapes turn a brighter purple, 7 to 15 minutes (depending on the size of the grapes).
In another bowl, add the ricotta, mascarpone, sugar and vanilla and mix until well combined.
Heat a grill pan on medium heat. Pour the remaining 3 tablespoons olive oil on a plate. Dip both sides of the bread onto the oil and transfer to the grill pan. Grill on both sides until grill marks appear, a few minutes.
To serve, spread the ricotta mixture on the crostini and top with the roasted grapes.
Bring the milk, half-and-half and salt to a simmer in a saucepan. Mix in the lemon juice and let the mixture sit off of the heat until curds form. Line a sieve with 2 pieces of cheesecloth and place it over a medium bowl.
Pour the milk mixture into the sieve and allow it to drain into the bowl for 20 to 25 minutes. Discard the liquid in the bowl occasionally so the sieve is not sitting in the liquid. The longer you let the mixture drain, the thicker the ricotta will be.
Use immediately or refrigerate in a covered container for 4 to 5 days.