The touch of cocoa powder in this streusel tempers the sweetness and adds a subtle depth of flavor—you won’t notice it’s there, but it gives the topping a little extra oomph. Cakes like this one freeze beautifully, so you can even make it up to a month in advance. The best accompaniments are a bowl of fresh fruit and a cup of good coffee.

Preheat the oven to 350°F and position an oven rack in the lower third. Lightly coat a 10-inch tube pan with a removable bottom with melted butter, oil, or high-heat canola oil spray, dust it with flour, and tap out the excess.

To make the streusel, place the brown sugar, cinnamon, and cocoa powder in a medium bowl and stir with a spoon until well blended. Smash any lumps of brown sugar or cocoa so the mixture is even in texture. Add the pecans and stir to blend.

Place the flour, baking powder, baking soda, and salt in a medium bowl and whisk to blend thoroughly.

Put the butter and granulated sugar in the bowl of a stand mixer and beat on medium-high speed until the mixture is very light, almost white in color, 4 to 5 minutes. You can also use a hand mixer and a medium bowl, though you may need to beat the mixture a little longer to achieve the same results. Scrape down the bowl with a spatula.

Crack the eggs into a small bowl and beat with a fork to blend. Add the vanilla and beat well. With the mixer running on medium, add the eggs to the butter mixture about 1 tablespoon at a time, blending well after each addition. About halfway through, turn off the mixer and use the spatula to scrape down the bowl; then continue using the rest of the eggs. Scrape down the bowl again.

With the mixer running on the lowest speed, add one-third of the dry ingredients. Just as it is barely blended and you can still see a few patches of flour, add half of the sour cream. Repeat, ending with the dry ingredients. Scrape down the bowl and finish blending the batter by hand.

Spoon half of the batter into a 10-inch tube pan with a removable bottom, and smooth the top. Sprinkle half of the streusel evenly over the batter. Spoon the remaining batter into the pan and level and smooth the top. Sprinkle the remaining streusel over the top. Bake for 65 to 75 minutes, until the cake is firm to the touch and a skewer inserted into the center comes out clean. Transfer to a rack to cool for at least 30 minutes if you want to serve it warm, or about 1½ hours to cool completely.

Run a thin knife or spatula around the inner tube of the pan to loosen the cake. Lift the center portion of the pan, with the cake, out of the ring. Run a thin knife or spatula around the bottom of the cake to release it from the bottom of the pan, Hold the cake firmly with your hands on both sides. Gently lift the cake, sliding it up the tube portion until it comes completely off the pan. Set it on a serving plate. Use a serrated knife to cut slices.

The cake will keep at room temperature for up to 4 days covered with plastic wrap or a cake dome. Once it has been cut, press a piece of plastic wrap against the cut edges to keep the interior fresh. The cake can be frozen, double wrapped in plastic, for up to 4 weeks. Thaw, still wrapped in plastic to avoid condensation, for 3 hours before serving. Remove the plastic, wrap in aluminum foil, and reheat in a 325°F oven for 20 minutes, or until warmed through.