In a food processor with a steel blade put flour, pecans, sugar, butter and salt and blend at high speed until the dough clumps .
Transfer the dough to a work surface and form a disc shape. Wrap in plastic wrap and refrigerate for about an hour.
Roll out the dough on a floured surface to about 3-4 mm thick and cut out 4 cm circles. Refrigerate.
Preheat oven 190c degrees.
In a medium saucepan put milk, sugar, butter and salt and heat to a strong boil.
Add flour and stir while cooking, until it turns into a lump of dough.
Transfer the dough to the bowl of an electric mixer with a paddle attachment and mix on medium speed for 2-3 minutes until it cools down a little.
Add the eggs gradually while beating until dough is elastic and smooth. Check the readiness of dough by creating a "trail" with a wooden spoon in the center of the dough - if the track remains stable, add some eggs, and if it closes a bit - the dough is ready. It is important not to add too many eggs to the dough or it may become too soft and ruined.
Transfer the dough to a pastry bag fitted with a round 1-2 cm piping tip. On a baking tray lined with baking paper pipe small cream puffs (about 3-4 cm in diameter). It's important to leave some space between the creampuffs.
Put a pecan streusel circle on top of each creampuff and lightly press it down.
Baking: bake for 12-15 minutes - is important not to open the oven door during this time.
Lower the oven temperature to 180c degrees and bake for another 7-10 minutes, until completely golden and set.
Cool completely before filling.
In a small saucepan put milk, sugar and vanilla and bring to a simmer.
In a separate bowl, whisk egg yolks and cornstarch until blended. If the mixture is too thick - add a teaspoon of cold water.
When the milk mixture is boiling remove from heat and add about 1/3 of it into the yolk mixture while vigorous whisking. When blended, return into the pan with the remaining milk and mix.
Continue to cook over medium-low heat, while whisking constantly, until a very thick pastry cream forms.
Transfer the cream into a sealed container and cover its top with plastic wrap to avoid crust from forming. Cool completely in the refrigerator.
Transfer the cold cream into a bowl and mix well with a whisk until it returns to the original texture. Add rum and continue to mix until uniform.
Whip the heavy cream to stiff peaks and gently fold into the vanilla cream until smooth.
Transfer the cream into a pastry bag with a 1 cm round piping tip and fill the puffs.
Garnish with powdered sugar and serve.
Keep the cream puff in a closed container in the refrigerator for up to 3-4 days, but they are at their best on the day or two after preparation.
You can use any other nut you like instead of pecans.