Make the streusel: Mix together flour, brown sugar, and salt. Using a pastry cutter or your fingers, cut butter into the flour mixture until small to medium clumps form. Cover and refrigerate until ready to use.

Cook lemon slices: In a large skillet of simmering water, cook lemon slices 1 minute. Drain and repeat. Arrange lemon slices in a single layer on a parchment-lined baking sheet.

Preheat oven, prep pan, and sift dry ingredients: Preheat oven to 350°F. Butter a 9-inch angel-food-cake pan. Sift together flour, baking powder, baking soda, and salt.

Beat butter, sugar, and zest: In a mixer fitted with the paddle attachment, beat together butter, granulated sugar, and lemon zest on medium speed in a large bowl until light and fluffy, about 2 minutes.

Add eggs and vanilla: Beat in eggs, one at a time, then the vanilla.

Add flour mixture in three additions: Reduce speed to low. Beat in flour mixture in three additions, alternating with sour cream, beginning and ending with flour mixture and beating until combined after each addition.

Assemble cake in pan: Spoon half of batter evenly into pan. Arrange half of lemon slices in a single layer over batter. Spread remaining batter evenly over top. Cover with remaining lemon slices in a single layer. Sprinkle chilled streusel evenly over batter.

Bake: Bake until cake is golden brown and a tester inserted in center comes out clean, about 55 minutes.

Cool and unmold: Transfer pan to a wire rack set over a baking sheet; let cool in pan 15 minutes. Run a knife around edges of pan and remove outer ring. Let cool on rack 15 minutes more. Run a knife around center tube. Slide two wide spatulas between bottom of cake and pan, and lift cake to remove from center tube. Let cool completely on rack.

Make the glaze: Just before serving, stir together confectioners' sugar and lemon juice in a medium bowl. Drizzle over cooled cake, letting excess drip down sides. Let glaze set before slicing, about 5 minutes.