Fresh
Usually sold in bulk.
When fresh, hazelnuts are sold in their green husk. To choose well, shake them. If you don't hear anything, that's a good sign! The kernel shouldn't shake against the side; if it does, it indicates the fruit is not properly formed.

Dry
Dry shelled hazelnuts are most often sold in bags or punnets in 125, 250, or 500 g quantities. They may also be sold already chopped or ground.

When dry, hazelnuts should have an attractive dark brown shiny shell, with no holes or cracks, no matter how small. 

Hazelnuts are sturdy. In the open air, dried or fresh, they'll easily keep in your fruit basket for several weeks, if conditions are not too damp or hot.

Keep them out of the refrigerator, which softens them and makes them prone to mold. Cold also congeals the oil they contain and they lose their flavor.

To store hazelnuts, spread them out in a dry airy place to dry. Once shelled, keep away from humidity and use within a short time. 

To crack fresh hazelnuts
Choose a nutcracker suitable for the size of the nut and take care not to crush it.

To remove the green part of fresh hazelnuts
Pinch forcefully at the slightly convex end to push the nut out. 

or
Place some shelled hazelnuts on a baking sheet and place them under the broiler for a few moments, being carefully they don't burn. Remove from the oven and cool to lukewarm. Rub them with a clean cloth; the skins that cracked under the heat will come off easily. 

Use hazelnuts whole, grated or ground to flavor savory and sweet dishes. They are easily toasted in a dry skillet to bring out their flavor. 

Finely ground, they can be used in place of flour to make a ‘torte’.

Roughly chopped, they add crunch to biscuits or meringues.

Use them as the basis for a stuffing or chop them up with some dried fruits and scatter the mixture onto your cereal.

Crush hazelnuts and use them to coat goat's cheese or fresh white cheese.

With their distinctive flavor and their affinity for chocolate, hazelnuts play a starring role in delicious chocolate cake and biscuit recipes.

Try them as a crunchy topping to salads or with sweet fried scallops.

10 hazelnuts = 14 g
250 ml / 1 cup whole hazelnuts = 135 g
250 ml / 1 cup hazelnuts, chopped = 115 g
250 ml / 1 cup hazelnuts, grounded = 75 g

In Italy
Hazelnut paste made from 200 g shelled hazelnuts and 200 g icing sugar is a staple of Italian sweet making. It is also an ingredient in gianduia, an Italian praline, made from icing sugar, toasted hazelnuts and milk chocolate. It is included in many pastry recipes, including fillings, mousses, spreads and ganache. 

In Turkey
A sauce made from garlic and hazelnuts is served as an accompaniment to shellfish.