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1
Adjust oven rack to middle position and heat oven to 350 degrees.
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2
Grease two 9-inch-wide by 2-inch-high round cake pans and line bottoms with parchment paper.
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3
Grease paper rounds, dust pans with flour, and knock out excess.
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4
Whisk flour, baking powder, baking soda, salt, and 1 1/2 cups sugar together in large bowl.
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5
In 4-cup liquid measuring cup or medium bowl, whisk together melted butter, buttermilk, oil, vanilla, rum extract, lemon zest, and yolks.
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6
In clean bowl of stand mixer fitted with whisk attachment, beat egg whites at medium-high speed until foamy, about 30 seconds.
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7
With machine running, gradually add remaining 1/4 cup sugar; continue to beat until stiff peaks just form, 30 to 60 seconds (whites should hold peak but mixture should appear moist).
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8
Transfer to bowl and set aside.
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9
Add flour mixture to now-empty mixing bowl fitted with whisk attachment.
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10
With mixer running at low speed, gradually pour in butter mixture and mix until almost incorporated (a few streaks of dry flour will remain), about 15 seconds.
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11
Stop mixer and scrape whisk and sides of bowl.
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12
Return mixer to medium-low speed and beat until smooth and fully incorporated, 10 to 15 seconds.
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13
Stir 1/3 of whites into batter to lighten, then add remaining whites and gently fold into batter until no white streaks remain.
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14
Divide batter evenly between prepared cake pans.
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15
Lightly tap pans against counter 2 or 3 times to dislodge any large air bubbles.
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16
Bake until cake layers begin to pull away from sides of pans and toothpick inserted into center comes out clean, 20 to 22 minutes.
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17
Cool cakes in pans on wire rack for 10 minutes.
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18
Loosen cakes from sides of pans with small knife, then invert onto greased wire rack and peel off parchment.
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19
Invert cakes again and cool completely on rack, about 1 1/2 hours.
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20
For Frosting:.
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21
In a medium bowl, cream the butter until light and fluffy.
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22
Add confectioner's sugar, pinch of salt.
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23
Beat, adding buttermilk as needed for consistency.
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24
Once buttermilk is incorporated, add extracts and beat well.
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25
Place first layer of cake on plate, spread with frosting.
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26
Top with approximately 1 cup of toffee bits.
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27
Place second layer on top.
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28
Lightly frost cake, making a crumb coat.
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29
Place in refrigerator for 30 minutes.
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30
Frost with remaining icing.
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31
Gently press toffee bits all the way around on sides of cake and sprinkle bits on top of cake for garnish.
