In a small saucepan, whisk 1 cup milk with 5 Tbsp flour.

Cook over medium heat until thick and bubbly, then cook for another minute.

Remove from heat and let cool.

Once cooled to room temperature, cover with wax paper and refrigerate until ready to use.

Pre-heat the oven to 425 degrees.

Mix the sugar and butter until light and fluffy.

Add the eggs and vanilla extract and mix until well combined.

Add the dry ingredients, mix well.

Add the milk and hot water, mix well.

Beat on a medium-high speed until smooth.

Drop spoonfuls of batter onto a greased cookie sheet.

Bake at 425 degrees for 8-10 minutes.

Cool on wire rack.

Beat the butter and sugar until fluffy.

Add the confectioners sugar and vanilla extract and beat until light and fluffy.

Gradually mix in the cooled flour/butter mixture, one spoonful at a time until completely mixed, making sure to scrape down the sides of the bowl on occasion.

Once mixed, beat on a medium-high speed until light and fluffy.

Spread the filling on one cookie and top with another.

Continue until the cookies are all filled.

Serve. Refrigerate left-overs.