Make the honey custard first so that it has time to cool.
Combine the honey, egg yolk and salt in a medium mixing bowl and whisk to combine (this will take a moment ... depending on your honey, it might be a sticky glob first, but keep whisking!)
Add the corn starch to the honey mixture and whisk in. Set aside.
Heat the milk over medium heat until it's barely simmering--don't let it boil.
While whisking the honey mixture, add about 1/3 of the milk. Whisk for a few moment before pouring the honey/milk mixture into the remaining milk in the pan and whisking without stopping.
Keeping the heat on medium, whisk until the custard thickens. Remove from heat and press through a sieve.
Add the butter to the strained custard and whisk to combine.
Place a piece of plastic wrap onto the surface of the custard to keep a skin from forming and place in the fridge to cool for at least an hour.
For the cake, heat the oven to 350 degrees Fahrenheit and position the racks toward the center.
Lightly grease and flour (or use Baker's Joy spray) two 4-inch round cake pans. Set aside.
Sift the flour, baking powder, baking soda, salt and cinnamon together. Set aside.
Beat the butter until light and fluffy in the bowl of your standmixer. Add the maple syrup.
The mixture might look curdled, but it's fine. Add the egg and vanilla and continue to mix.
Alternate between adding the dry ingredients and milk, scraping down the bowl as needed.
Measure out 2 tbsp of the toasted pecans into a small bowl and add about 1 tsp of flour. Toss to coat (this will help keep the pecans from sinking to the bottom). Set bowl aside.
If your cake batter still looks a bit lumpy, remove the bowl from the mixer and hand whisk it for about a minute--the batter will come together quickly.
Add the pecans tossed in flour and whisk lightly to combine.
Divide the batter between the 2 cake pans evenly and bake for 20-25 minutes.
When finished baking, cool in the pan for 20-30 minutes (if the pan is cool to touch, it's safe to turn the cakes out).
Remove the cake layers from the pans and finish cooling them on the wire racks.
For the frosting, cut the butter into even pieces. Place in a sauce pan that does not have a dark colored bottom (you need to be able to see the color change).
Heat over medium and melt the butter. Do not leave the butter unattended, because the butter's milk solids can burn, and then you'll need to start over.
Continue cooking until the butter smells nutty and the milk solids have dropped to the bottom of the pan and are light brown. Remove from the heat immediately and set aside to cool.
Once cooled, add the brown butter and vanilla in the bowl of your stand mixer with a 1/2 cup of confectioners sugar, mixing to combine. Gradually add the remaining sugar in 1/2 cup increments, as well as the heavy cream in single tablespoon increments.
The frosting will look gritty before it looks smooth, but don't worry. It will come together. Once you've added all the sugar and all the cream, whip on high for a few minutes.
To assemble, place the bottom layer on a cake round. Trim the top off to make an even layer.
Using some of the brown butter frosting, pipe a border to keep the honey custard in, around the top edge of the first layer.
Add the honey custard within the frosting border; you will have extra, so don't overfill.
Trim the top off the second layer, turn it cut-side down and place on top of the filling. Place in the freezer to chill for about 20 minutes.
Apply a crumb coating of brown butter frosting. Chill for 20-30 minutes in the freezer.
Reserve approximately a 1/2 cup of the frosting to pipe a border along the top and bottom of the cake, using a small French tip. Then, use the remaining frosting to cover the cake, evenly coating the sides and top. Smooth the frosting, though it doesn't need to be perfect.
Spoon on some of the extra honey custard on top and spread it gently, but don't let it run down the sides.
Sprinkle the reserved pecans onto the custard, covering evenly.
Pipe a border around the top of the cake and the bottom.