Mix flour, brown sugar, and cinnamon in a medium-sized bowl. Cut in butter until the mixture resembles coarse crumbs. Add in the pecans. Set aside.
For the cake
In a large mixer bowl, beat the sugar, butter, and sour cream for a few minutes until light and fluffy. Add the eggs one at a time, beating well after each. Scrape the bowl as needed. Beat in the vanilla.
Gradually beat in the flour and baking soda on low speed until blended. Scrape the bowl down to the bottom to make sure all the flour is mixed in.
Spread half of the streusel into the bundt pan, evenly all around. Pour/spoon half of the batter evenly over the streusel. Over that, sprinkle the other half of the streusel. Cover that carefully with the remaining half of the batter. Smooth the top.
Put it in the oven on the middle rack. Check it at about 45 minutes. If the top is browning too quickly, cover it lightly with foil. Bake for about one hour total, or until a toothpick inserted in the center comes out clean (I like to check it with the toothpick in a few other spots too, just to be on the safe side).
Cool the cake in the pan for only ten minutes. Invert it onto a cooling rack to finish cooling. If you like, glaze the cake, but only after it is completely cooled.
For the glaze:
In a medium bowl, using about one and a half cups of sifted confectioners' sugar, stir in two to three tbsp. of heavy cream. Continue adding additional cream, just a teaspoon or so at a time, until the desired consistency is reached. Keep stirring until all lumps are removed and the glaze has achieved the texture you like. Want it thicker? Add more confectioners' sugar, a bit at a time. Flavor the glaze with almond extract or, if you prefer, with vanilla extract. Probably no more than 1/2 tsp. is needed at most, depending upon the strength of your extract and your own taste. Generously drizzle on the glaze, evenly all around, letting it drip down the sides of the cake.