Preheat your oven to 350°F (180°C). Line a 9x13 inch baking pan with parchment paper.
In a large bowl, beat the 1 cup unsalted butter and 1½ cups granulated sugar together for about 3 minutes until light and fluffy.
Add the 3 eggs one at a time, mixing well after each addition. Mix in the 1 tablespoon vanilla extract, 1 teaspoon almond extract, and 1 cup sour cream.
In a separate bowl, whisk together the 2 cups all purpose flour, 1 cup almond flour, 1 teaspoon baking powder, and ½ teaspoon salt.
Add the dry ingredients to the wet ingredients and mix just until combined. The batter will be thick and creamy.
In a small bowl, stir together the ¼ cup melted butter, ⅓ cup brown sugar, 1 tablespoon milk, and ½ teaspoon almond extract. Stir in the 1 cup sliced almonds until coated.
Spread the batter evenly into the prepared pan. Scatter the almond topping evenly over the batter.
Bake for 38 to 45 minutes until golden brown and a toothpick inserted into the center comes out clean. Cool completely before slicing into bars.
If using the glaze, whisk together the 1 cup powdered sugar, 2 tablespoons cream, ½ teaspoon vanilla extract, and pinch of salt until smooth.
Drizzle lightly over the bars. Dust generously with powdered sugar before serving.