Layers of streusel and frangipane, an almond-based pastry filling, top this rich coffee cake. Martha made this recipe on Martha Bakes episode 605.
Preheat oven to 350 degrees. Make the streusel: Mix together flour, chopped pecans, brown sugar, and coarse salt. Mix in butter with a pastry blender or your fingers until mixture forms clumps. Cover and refrigerate until ready to use.
Make the frangipane: In bowl of food processor, combine pecans and granulated sugar and process until finely ground. Add butter, egg, flour, bourbon, fine salt, and vanilla, then process until smooth. Cover until ready to use.
Make the cake: Butter a 10-inch tube pan with removable bottom. Sift together flour, baking powder, baking soda, and fine salt into medium bowl. In bowl of electric mixer fitted with the paddle attachment, beat butter and granulated sugar on medium speed until pale and fluffy, about 2 minutes. Add eggs, 1 at a time, beating well after each addition, then add vanilla. Reduce speed to low. Add flour mixture in 2 batches, alternating with sour cream; beat until just combined.
Transfer batter to prepared pan. Sprinkle half of chilled streusel mixture evenly on top. Add half of frangipane; spread evenly with an offset spatula. Repeat using remaining streusel and frangipane.
Bake until coffee cake is golden brown and a cake tester comes out clean, about 60 minutes. Transfer pan to a wire rack set over a parchment paper-lined baking sheet to cool 15 minutes. Run a knife around edges of coffee cake to loosen, then use tube to lift coffee cake out of pan. Let cool on rack 15 minutes more. Run a knife around center tube. Slide 2 wide spatulas between bottom of cake and pan, running a spatula all the way around to loosen, and lift coffee cake to remove from center tube. Let cool completely on rack.
The coffee cake can be stored at room temperature, covered, up to 3 days.