Line the hazelnuts in a large rimmed baking sheet and bake at 350F (180C), for 10-15 minutes stirring every 5 minutes.
Using the microwave
Line a paper towel over the bowl and evenly spread the nuts.
Roast for 4-6 minutes using 2 minutes increments.
Using the stove
Place the nuts in a wide skillet and cook over medium heat for 3-4 minutes while stirring.
Adding flavor
Mix the nuts with the oil (1 tablespoon of oil per 1 cup of nuts) then mix in your choice of flavor and bake using the oven method.
Notes
When warm, the nuts are chewy allowing them to reach room temperature before using and eating.
Use your sense of smell and sight to determine if the nuts are ready, when your kitchen is filled with a pleasant nutty aroma and the nuts are golden brown then they are ready.
Your oven, microwave, and stove are different than mine. The time needed to roast or toast the nuts may vary. Pay close attention to their smell and color.
Pay close attention to the nuts as the roast/toast. The transformation from lightly baked to completely burnt is very fast.
Best to store the nuts in a dark and dry place in your pantry for up to 4 weeks. A freezer is also a good option for up to 6 months.
To prevent the nuts from rolling all over the place as you chop, place the cutting board in a large rimmed baking pan.