Prep:Preheat oven to 350°F (175°C). Lightly grease and line an 8-inch (20-cm) square pan with 2 strips of parchment paper, in a crisscross pattern. Allow the paper to hang over the sides, so you can easily lift out the bars once baked.
Make:Mix oats, coconut and peanuts in a large bowl. Set aside. Whisk melted butter with honey, salt and vanilla. Pour the mixture over the oats. Stir thoroughly with a spatula until all of the dry bits are covered. Transfer this mix to the baking pan and press it in tightly and evenly. (I use the back of a measuring spoon or a glass to get an even surface.)
Bake:Bake in the middle of the oven for 20 minutes, until the top is golden brown. Allow to cool completely in the pan, then continue cooling in the refrigerator for another 30-60 minutes. Pull the whole block out of the pan and slice it into 12 rectangular bars using a very sharp knife.
To make chocolate bars, add chocolate to a heatproof bowl and place it over a pot of simmering water. Cook, stirring occasionally, until it’s almost completely melted. Remove from heat and allow the last bits to melt.
Dip bars into the chocolate. Place them on a baking sheet or plate (chocolate side up) and transfer to the refrigerator. Chill until the chocolate is set. Once chilled you can stack the bars or place them in a container. Keep granola bars in the refrigerator and eat within a week.
Notes
Make sure the granola bars (well, one large bar) are completely chilled before slicing. Because butter is a main ingredient, the bars soften at room temperature. That's why slicing them is the easiest when they are very cold.
You can use other nuts and seeds when making these. I love sunflower and pumpkin seeds, sesame seeds, dried fruit and puffed rice.
The chocolate dip is completely optional, but it does make these very tasty.