Combine honey and egg whites in a heat safe bowl. Place bowl over a pan of boiling water, and make sure the bowl does not touch the boiling water. Heat mixture for about 4-5 minutes, or until it reaches a temperature between 150° and 160°.
Remove from heat and immediately beat with the whisk attachment of a stand mixer or beat with a hand mixer. Beat on the highest speed until mixture has cooled, is fluffy and stiff peaks form. This should take 10-15 minutes.
Using the paddle attachment, slowly add the butter. Beat mixture on high for several minutes until light and fluffy.
Add the raspberry preserves and continue mixing until thoroughly combined.
To assemble the cake, add buttercream to each cake layer (or follow the variation below) and then stack the layers. Frost the top and sides of the stacked cake with the remaining buttercream.
Leftover buttercream can be refrigerated or frozen. When ready to use, simply beat for a few minutes until fluffy.