In a blender, puree the herbs and oil until completely smooth. Put the mixture in a saucepan and bring it to a simmer over moderate heat. Simmer for 45 seconds, then pour through a fine-mesh strainer into a bowl. Don't press on the mixture, but you can tap the strainer against your hand to get the oil to drip through faster. Immediately strain the oil again through a flat-bottomed paper filter. If the filter clogs, you may need to change the filter partway through.
It's okay to pick the filter up and squeeze it gently to get the oil out faster, but be careful not to break the filter. Sometimes a little dark liquid comes through the filter first. Don't worry; that's water. It will settle to the bottom because it is heavier than the oil. Let the filtered oil settle for a few hours, then pour it off the dark liquid. Store in an airtight jar in a cool, dark place.
This recipe gives the basic method for making a flavored oil from any herb. Because herbs vary in intensity from season to season (they tend to be mild in the spring and stronger in the fall), it's not possible to give you a recipe that will always have the perfect level of flavor. A good solution is to make a concentrated essence, and then dilute it with olive oil until I got the strength of character you like. Don't use extra virgin olive oil for these infusions because you want the herb taste to be more pronounced than the olive taste.You'll need a blender for this recipe; a food processor does not grind the herbs fine enough. The oil passes through the filter faster if it's filtered while still hot, so set up your filter before you start the recipe. You'll need a flat-bottomed paper filter, like those used for some drip coffee machines. Cone-shaped filters tend to get clogged.