Preheat oven to 350°F. Grease and line an 8x8-inch square or round baking pan with parchment paper.
In a stand mixer fitted with a paddle attachment, combine flour, sugar, cornstarch, almond flour, baking powder, baking soda, salt, and cinnamon.
Add the softened butter and mix until the mixture resembles fine sand.
Slowly stream in the canola oil while mixing on low speed.
In a separate bowl whisk together egg, egg yolk, vanilla bean paste, almond extract, orange zest, buttermilk, and sour cream.
Add the wet ingredients gradually to the dry mixture on low speed, mixing only until just combined.
For the frangipane, beat together the butter, sugar, and salt on medium speed until smooth.
Mix in the egg and almond extract.
Fold in the almond flour until a thick paste forms.
Spread the cake batter evenly into the prepared pan.
Dollop frangipane over the batter and gently spread into an even layer.
Sprinkle with toasted sliced almonds.
Bake for 30–40 minutes, or until golden brown on top and a toothpick inserted into the center comes out with a few moist crumbs. (If the top seems to be getting to browned, loosely tent the cake with foil during the final 10–15 minutes.)
Remove from oven and cool completely before slicing.
Dust with powdered sugar before serving, if desired.