1. Preheat the oven to 300 degrees.
2. Line three 9-inch layer pans with wax paper and oil the sides and bottoms.
3. Beat together the honey, butter, egg yolks, and vanilla. Add the coffee. Sift together the whole wheat flour, baking soda, and salt and stir in alternately with the buttermilk.
4. Beat the 6 egg whites until stiff but not dry and fold into the cake batter. Divide among the three pans and bake for 30 minutes or until cake tests done. Cool on wire racks.