Step 1

Pre-heat oven to 350 degrees. Grease the bottoms of two 8-inch pans. Line the bottoms with parchment, then grease and flour the parchment and sides of the pans. Set aside.

Step 2

Remove 1/3 cup flour and set aside.

Step 3

Sift together the remaining flour, baking powder, cinnamon, and salt. Set aside.

Step 4

Using an electric mixer, beat the butter until smooth. Add the sugar. With the mixer on medium speed, cream the sugar and butter together until light and fluffy. Add the vanilla extract.

Step 5

With the mixer on medium-low, mix in the eggs, one at a time. Stop the mixer and scrape down the sides of the bowl.

Step 6

Working in alternating batches, mix in half of the dry ingredients followed by the milk. Add in the second half of the dry ingredients and mix until just combined.

Step 7

Toss the diced apples with the reserved flour. Fold in the apples and pecans until evenly distributed.

Step 8

Divided the batter between the two pans. Bake for 32 to 35 minutes until golden on top and a thin knife inserted into the center of the cakes comes out clean. Cool on a wire rack for 15 to 20 minutes before removing the cakes from their pans.

Step 9

Raise the oven temperature to 375 degrees. Line a baking sheet with parchment or silicone baking mat and set aside.

Step 10

Combine all of the ingredients together in a medium bowl. Stir together with a wooden spoon.

Step 11

Spread the mixture out on the prepared pan. Bake for 8 to 10 minutes, stirring halfway, until the crumbles are golden brown. Let cool and break into small pieces before use.

Step 12

Place egg whites and sugar into the bowl of an electric mixer. Whisk briefly by hand until combined.

Step 13

Fill a saucepan with a few inches of water and bring to a simmer over medium heat. Place the mixer bowl on top of the saucepan to create a double-boiler.

Step 14

Whisking constantly, heat the egg mixture until it registers 160 degrees on a candy thermometer. Once hot, carefully return the mixer bowl to the stand mixer.

Step 15

Using the whisk attachment, whip the egg white mixture on high speed for 8 to 10 minutes until the bowl is no longer warm to the touch and the meringue is fluffy, glossy and holds a stiff peak.

Step 16

Stop the mixer and swap out the whisk attachment for the paddle.

Step 17

With the mixer on low, add in the vanilla, cinnamon, and butter, a couple tablespoons at a time.

Step 18

Once all of the butter has been added, turn the mixer up to medium-high and mix until silky smooth. NOTE: If the mixture looks curdled, just keep mixing until it is smooth (this could take up to about 5 minutes). If it appears soupy, place the mixer bowl in the fridge for 10 to 15 minutes, then mix until smooth.

Step 19

Melt the butter in a saucepan over medium heat. Once melted, stir in the brown sugar and corn syrup. Turn the heat up to high. While stirring with a wooden spoon, bring the mixture up a boil and cook for about 5 minutes or until the sugar dissolves.

Step 20

Remove from the heat and carefully whisk in the cream. Reduce the heat to low. Place the sauce pan back on the stove and whisk, slowly but constantly. Simmer for about 8 minutes.

Step 21

Remove from the heat and add in the remaining ingredients. Place in a heat-safe container and allow to cool and thicken.

Step 22

After the cakes have completely cooled, carefully slice them in half horizontally with a long serrated knife. Place one of the bottom layers on a cake board or cake pedestal. Spread on about 1 cup of the buttercream then sprinkle with ½ cup of the crumble. Top with the next layer of cake and repeat. Frost the stacked cake with the cinnamon buttercream and set in the refrigerator to chill for 15 to 20 minutes.

Step 23

After the toffee has cooled but still liquidy, carefully drip the sauce around the edges of the chilled cake. Pour into the center and use an offset spatula to smooth out. The toffee sauce is a bit thicker than regular caramel, so be careful not to pull and mix with the buttercream when spreading across the top.

Step 24

With any remaining buttercream, mix in a couple tablespoons of the leftover toffee sauce, or to taste, to create a toffee buttercream. Pipe on top of the cake using an open star tip and sprinkle with chopped pecans or leftover crunch.