Combine the apples, currants, pecans, brown sugar, and cinnamon in a small bowl.
Set aside.
To make the cake:
Preheat oven to 350°F (175°C). Grease and flour a 9-inch round cake pan. (Or use a cooking spray with flour, like Baker's Joy or Pam Baking.)
Whisk together the flour, baking powder, baking soda, and salt. Set aside.
Using an electric mixer on medium speed, beat the butter, sugar, and brown sugar until light and fluffy. Add the eggs and vanilla, and mix well.
Decrease mixer speed to low. Add the flour mixture in three portions, alternating with two portions of sour cream. Mix just until combined.
Transfer half of the batter to the prepared pan and spread evenly. Sprinkle the streusel mixture evenly over batter. Spread the remaining cake batter evenly over the streusel.
Sprinkle the top of the batter with toffee bits.
Bake 45 to 50 minutes, or until a pick inserted into the center comes out clean.
Cool in the pan for 10 minutes, then transfer to a serving plate. Or, cool completely in the pan if serving directly from the pan.
To make the glaze:
Combine the confectioners' sugar, 2 teaspoons of milk, and cinnamon in a small bowl. If necessary, add more milk until the glaze is the desired consistency.
Drizzle the glaze over the cooled cake.
Notes
Recipe adapted from an unidentified recipe clipping.
Store in an airtight container at room temperature for 3 or 4 days.