Combine garlic, fennel and oil in a heavy saucepan. Bring mixture to a boil and then reduce to a simmer. Simmer until fennel and garlic are very tender, 45 minutes to an hour. Remove from heat and allow the mixture to come to room temperature. Strain oil, pressing on solids, into a clean bottle and refrigerate.
Remove tender garlic and fennel from strainer. Mash mixture and season with salt and pepper. Use as spread for crostini or crackers