Using a food processor or a dough cutter (or a fork), combine unsalted butter, flour, sugar and salt until loosely combined

Slowly add the cold water and watch until it begins to clump together. Once this happens stop pouring water and stop the machine or mixing.

Roll the dough into a ball and then into a thick disk shape. Wrap in plastic wrap and place in the refrigerator for at least 30 minutes or up to a day.

Roll out on a pastry sheet or counter top using a dusting of flour and sugar. Roll out until the proper size has been achieved for your tart pan.

Rub unsalted butter over the pan's sides and bottom to prevent the tart from sticking.

Place the dough in the pan. Gently press the dough into the bottom corners and then using a rolling pin, roll it across the top of the pan to create a clean, even edge

Preheat the oven to 400 degrees Fahrenheit.

Combine the chopped rhubarb and strawberries into a mixing bowl. Add the sugar, flour, nutmeg and salt. Mix to combine and set aside while you make the crumble topping and roll out the dough.

Once the dough is rolled out, place the filling into the tart pan - filling as much or as little as you prefer.

Dot the tart with 1 tablespoon of unsalted butter.

Melt the butter in a sauce pan. While the butter is melting (low-medium heat), mixing the dry ingredients in a mixing bowl - oatmeal, flour, sugars and salt.

Once the butter has melted, turn off the stovetop and remove the saucepan from the heat. Add the dry ingredients to the butter and stir to combine.

Place the topping on top of the filling and the butter dotting the top.

Place into the oven for 30-40 minutes. Remove once tart edges are nicely brown. Enjoy warm with a dollop of vanilla gelato or ice cream and a hot cup of tea.